Coworker is rude and it feels like their sabotaging my job

Sorry for the rambling post - kind of venting here but would love advice haha.

I’ve been in a new role for about three months now. When I first started, my coworker seemed very kind and helpful. I was super excited about the whole team. After a few weeks, I noticed she stopped making any eye contact with me when I would say hi or “have a great night” or anything else... Whatever. I can deal with that. Then, any time I tried to make small talk or ask a question, she would give a one word answer and walk away to start whispering with another coworker (feels very “high school”). Again, not a huge deal. I can deal with people not liking me. I’ll just keep my head down, work hard, and be polite as usual.

Unfortunately, it’s only escalated. Now, she goes out of her way to hurry and finish MY assignments before I get the chance and sends them to our boss with me CC’d. Definitely doesn’t make me look great. Today I went to update some stats on a document (one of my responsibilities) and noticed it was locked by her. I went to ask her about it and she said she was basically already done updating so I shouldn’t bother. She also will share important updates/plans that affect the team with everyone but me. I believe she complained about me to our boss and manager as well. They had a talk with me and mentioned that coworker is going above and beyond in areas that I should be. I wanted to explain that I’ve only been in the role for two months and haven’t felt super supported but chickened out for fear of conflict. I certainly don’t want to cause issues this early, I’ve just been trying to work extra hard. Our boss and manager also LOVE her and she was recently promoted.

I’ve never had a conflict with a coworker before. I show up, I try to be kind to everyone, and I work hard. However, this is my first professional post-grad job in person. I have worked only remote since graduating, so this is new territory. I’ve just never experienced anything remotely close to this. I’ve been racking my brain for anything I might have done to upset her and it’s driving me crazy. The only thing I can think of is that she runs our social media accounts and one of my first assignments was to perform a social media “audit” for new ideas, anything that could be updated, etc. I also had to present it to the team.. I could see why that might make her uncomfortable but none of that was my choice. It was a directive from our manager.

What would you do? Keep working hard and hope it blows over? Talk to her directly? Lightly mention how I’m feeling to our boss? HR? I’m really scared of causing any “drama” but I also want to feel comfortable and set up for success in my role.

Thanks to anyone who read this, and thank you in advance for any insights or advice you can offer.