Am I wrong for "taking advantage" of my sister?

I'm going to keep this as brief as I can, but it's a long story. Basically, I'm a female in my thirties and have just one sister, who is almost 4 years older. We got really close around the time she got married and moved out, which was 20+ years ago. We've had our ups and downs, but always been there for each other, and I've long thought of her as my best friend. She got married young and started having kids right away, so all three of hers are older. I got married 3 years ago and have an infant (under a year old).

Right at the beginning of COVID, she and her husband bought a house with acreage while the market was down for a price we'll never see happen again. They've since been able to pay off the house, make significant improvements, put up a pole barn, etc. About a year in to lockdown, when the market went up, my parents' landlord sold their long-term rental, and they needed somewhere to go. My sister and BIL gave them some of their land to place a house, and they've been living here ever since. Around that same time, I had to move back home from another city because of serious health issues. I met my husband a year later. We had an apartment, then found a house we thought was our forever home, and were in a rent-to-own arrangements. Because of landlord negligence during my pregnancy, we had to leave on short notice in order to avoid a health threat before we had a newborn at risk, and housing costs being what they are, we had nowhere else to go but back with my parents.

Since then, my parents have asked us to stay permanently. They can't make ends meet now that they're retired, we help out with things they're too old to manage on their own, and they give us an extra hand with our baby. It's far from ideal, and we've had lots of ups and downs, but we finally had a solution in mind.

See, the "gift" of the land wasn't actually a gift. The arrangement was for my parents to sign the house over to my sister and BIL when they can no longer live independently, so the land still belongs to them, and the house will someday too. And I get it, they want their kids close by someday, so we had agreed to vacate at that point; all my parents requested was that they "purchase" the house for a small amount that would then allow my husband and I to get a start somewhere else. We were going to put a small addition on the house to make it a little more reasonable for two families to share, and hoped to get a portion of our investment back when we inevitably had to leave.

A few days ago, sis and BIL came over and informed us that they didn't want to keep that arrangement. They didn't want us to put an addition on the house that they, quote, "didn't want or need", as if the house was already theirs. They didn't want to pay anything to us at the end of our time living here caring for our aging parents. My sister then told us that they didn't "want to pay for you to be comfortable". She also stated that, if she'd known I would be here a few years down the road, they wouldn't have let my parents put the house here. They suggested they just buy the house now, and we all leave to find something that worked better for two families.

We were all kind of flabbergasted, because we'd spent months going back and forth about this and they'd had dozens of opportunities to tell us they didn't want us staying here. My husband and I even passed up an opportunity to move out of state and buy a cheap house from his family in order to stay and care for my parents (which I posted about on here before), and my sister didn't tell us back then that she wanted us out. They tentatively agreed to the plan to buy us out, so to speak, then said they'd never wanted to do that in the first place. My parents clearly don't want to move at their age, especially after all the hard work they've put into this place, and my sister knows it. I was very hurt, because it was clear that they took issue with me specifically living here, to the detriment of my husband and son and our parents. I asked her to sit down and talk in an effort to clear things up and mend fences a bit.

During that conversation, among a lot of other things, she told me that I'd been taking from her my whole life. She brought up a toy of hers that my mother gave me when I was a toddler as an example of favoritism, and asked how many pictures of her were up in our parents' house. My mom has a picture wall that highlights the current events for our family; for the last twenty years, it's been all my sister and her kids. Now, there are still pictures of all of them, but at the moment, yes, there are more of my wedding and my son because that's the newest big family events. I was absolutely confused, because I'd always thought our relationship was reciprocal. But according to her, I exhaust her because I'm impossible to tell I'm wrong, disturb her peace, and have been taking advantage of her my entire life. She said she's felt obligated to do things for me, that I had an easier childhood than she did, and that I've always gotten more from our parents. I brought up the fact that she and her husband moved in with us twice earlier in their marriage when they were struggling, that I got up every night with her kids and sacrificed space and privacy to share my bathroom with their entire family, not to mention the rest of the house. I reminded her that we devoted mountains of time and energy and thousands of dollars to their family over the years because I genuinely thought that's what family does. The person with the most need gets the most help, and now circumstances have changed.

Then she said I felt entitled to live on her land because we were going through a hard time, and I just couldn't handle it anymore. I was so shocked that what I'd thought was my closest friend had apparently resented me for decades, that everything she did for me that I cherished was out of a sense of obligation. I snapped that it obviously wasn't my dream to live with our parents, that it was ridiculous to insinuate that I was somehow trying to scam her out of money, and said I was done before getting up to walk away. She followed me into my bedroom, where I loudly told her that she needed to leave; she grabbed the door knob and held it shut to prevent my husband from coming in. That's the point when I lost it, I yelled that this was still our room and our home and she needed to get out. She finally did, but not before telling me she hopes I get some therapy for my narcissism. (For the record, I am in therapy, but for postpartum depression)

Now I'm looking back on all the years of leaning on each other and wondering if I leaned too hard. Did I ask too much of her? Did I expect too much? Ironically, if they had followed through with the plan to "buy" the house years from now and my parents gave that up front money to my husband and I, it would be significantly less expensive than buying the house outright now, so I doubt this is about money. I definitely lost my cool and raised my voice, but I genuinely thought our relationship was that of close family that loves and looks out for each other. I know she wanted to keep going, and said I was twisting everything she said to make it worse. AITAH?