Cousin hates me & has a serious insecurity, jealousy problem

Five points for best advice.

A little cousin, who asks me to hang out or contact me pretty often abruptly stopped talking to me and began to act weird; I think it’s my other cousin, Anna's fault.

Anna and I are both adults, (she's older than me) but she hates me because she's very insecure and I inadvertently make her jealous and competitive. I wish I was exaggerating but I’m not.

Her mom constantly compares her to me and her smart brother. There's not much to compare to me, she's better at me at a lot of things but she's aiming for EVERYTHING.

I’ll spare the details but basically she compulsively copies me at everything including big life decisions. (Which even our skeptical friend notices and finds hilarious). When she copies me, people raise an eyebrow because they don’t expect her to do those things. She’s polar opposite of me. She has thrown away a lot of money for the sake of buying the same thing I did or something better. If it wasn’t right away every single time, then I wouldn’t care or be creeped out.

We worked together for a long time. I always hide my birthday from everyone, but my boss revealed it one day. So two parties were thrown for me much to my annoyance. Every time, she avoided me and sulked. She's only like this for my birthday, not the other coworkers, and definitely not hers.

She is very competitive and territorial over friends, even the ones I have known longer. She’ll even start trying hanging out with people who she finds annoying if those people are my friends. I had two friends go: “Uh, your cousin has been asking me to hang out a lot recently.” And “Oh she didn’t invite you? But she invited everyone, including me surprisingly and she was mad that I didn’t go…. I don’t even fit in with them.”

If I’m around, she gives me this weird look while she’s with them or talking about them. This happened numerous times. A friend of ours noticed it and became worried.

She’s even possessive of OUR little cousins, which is ridiculous.

While she brags to me about being close with our friends and cousin, I kept my relationship with those people a secret but those people usually accidently tell her. But one time I let it slip about our cousin and I talking on the phone regularly, she had a mini meltdown, tried to hide it and kept asking me questions.

Right after that, our little cousin oddly stopped calling me, and she acted weird when I tried to talk to her. She’s very young, not even a teenager so I can imagine her believing what adults tell her.
Same thing happened to a friend.

If it wasn’t for the perfect timing and my cousin’s problem, I would just assume that they’re not interested anymore.

Anna has been much nicer to my face for the most part probably because she cares a lot about her reputation/popularity. Also, when she thinks I don’t see her at school, I can actually see her staring at me from the corner of my eye. Otherwise, she enthusiastically says hi to me and asks me about what I’m doing with my life.

She found out about her big crush trying to date me over a year ago which I kept a secret from her.
How bad is it? Some of our close friends started to notice after not believing me at first. It’s her and my older sister that has a competitive streak problem, but my sister is improving and taking therapy for I’m not sure what exactly.
I actually don’t see this problem in my male relatives who are laid back.

My mom knows about her but says she will just deny it.
Am I wrong to be suspicious? Should I ask those people who suddenly started evading me? How should I act around her?

Wait. I already posted this topic. For some reason it wouldn't show up in my post history. I don't know how to delete it.