private lending?

This is a ridiculous post, particularly for this subreddit, but I've learned a lot from the people on here just from lurking here, so I'm reaching out for advice. Hopefully, this is allowed.

I'm a full-time caregiver for my recently disabled girlfriend. We live together, her dad currently pays for all of her expenses and the apartment (we have to live away from them since she's severely immunocompromised). He gives me a stipend of 2000 a month for my own expenses, although often it just goes to supporting her, as I make my own money through a variety of gig jobs. Altogether, we don't live a super fancy life, but it's working thus far. I'm hoping to take over fully at some point the future.

All that said, her birthday is approaching (the 13th), and she's been feeling down lately. Her health has taken a few bad turns and she's struggling with being so young (I'm 27, she's 25) and fully disabled. I wanted to really treat her, she wasn't expecting anything besides me making her favorite dinner. Instead, I had a ton of plans, but her dad messaged me a couple of days ago saying he wasn't going to be able to cover the expense of her infusion this week, which is 400 dollars. I get why he couldn't, it's a very understandable issue he ran into, so I'll be able to cover it but it's going to end up ruining her birthday.

My question basically revolves around this: I have bad credit due to some financial irresponsibility in my early 20s, and now my income is so irregular that all of the lending companies I've reached out to over the past couple of days have denied me. I unfortunately don't have anyone in my personal life to ask, my parents and sister are all dirt poor and our friends our struggling like a lot of people in the US at the moment.

Are there private lenders or personal lenders that work on a more personal basis with people? Something similar to the borrow money pages on here, which I would be using if my account qualified, but I'm not much of a poster. Essentially I'm just looking for places that are legitimate that connect lenders and borrowers on a personal level. Ultimately, I'd pay a pretty big return for this type of thing too. I've been planning her day for weeks and really no one in the world deserves a good day as much as she does, so high-interest stuff would be manageable for me.

Additionally, if anyone has any other ideas on how to scrounge up a few hundred bucks quickly, that'd be helpful too!