Your mum is being a douche. Buy a bikini you love and wear the fuck out of it!

Pick up a bunch and try them on in the shop, find one YOU are comfortable with and don't bother thinking about what your mum will say. If she doesn't have anything nice to say she's not worth listening to.

(I don't know you or your situation but I'm plus size too and it can really suck to have someone screw with your body confidence. Personally, I know I really need to lose weight but that's not an overnight thing. I need to be confident with what I have right now because it's the days that I feel that confidence that give me the energy to be active and eat well. When that confidence is rocked (like every second day) it throws all my positivity out the window and I really struggle to get it back. I'm absolutely NOT saying you need to lose weight - maybe you do, maybe you don't - like I said I don't know you and everyone's body is different! Just throwing my own feelings out there.)

You gotta find that confidence and run with it - you'll look fab!!