I have a question

I work at this bank where it’s me and a few other girls. The first couple years that I worked there we were all pretty close we kind of became friends not just coworkers, so when Christmas will come around or someone’s birthday we would throw like a small celebration for someone’s birthday or for Christmas. But I got to the point somewhere along the way that all my coworkers just suddenly started talking crap about me almost like were in high school Patty behind the back I’m going to be nice to your face type a thing. I don’t feed into it I’m in my 30s I grew out of that shit a long ass time ago. But my question to you is a coworker‘s birthday is coming up and everything in between all of us girls has been OK for the last several months but now one of my coworkers just like oh what do you want to do for her birthday this year you want to get a cake and buy her gift and blah blah blah. Should I feel obligated to get her a gift even though they never once buy me a Christmas gift or birthday gift when the time comes. I might be the only one not doing anything for herWhen she was the one that I’ve spent the most money on for her birthday last year and for Christmas last year and she never got me anything or said happy birthday to me because she was being a fucking bitch. Should I be made to feel guilty by my other coworkers for not doing anything for the girl that’s a fucking bitch to me