So stressed out over MIL.

I'm 14 weeks pregnant with twins and my MIL has consistently tried to tell me what I should and shouldn't buy. In fact she has bought a handful of things from garage sales even after I had asked her not to for safety reasons. She continues to undermine anything I do or say and always tries to one-up my mother. Is it so bad that I want to choose the products I use for my own babies? She has taken away a lot of the fun and excitement during my pregnancy already. I'm at my wits end.