It may be that she's not being malicious, it's probably that she's superstitious and of that mindset - and everyones different and entitled to their opinion. However, this is clearly putting stress on you and she shouldn't continuously project her views on you, especially if she knows you're happy to buy things. So just tell her assertively that you appreciate her looking out for you and baby, but it's not something you believe in, what will be will be, and that you need her to respect your wishes even if she doesn't agree with it. If she continues to make comments, just distance yourself from her or walk away and tell her you don't want to hear any more of it - be quite assertive. Good luck
@Darcey thank you. Xxx
Tell your partner and if he doesn't help or put his mother in her place then frankly I'd be telling to go and f*ck herself and that if she carries on, she wouldn't be allowed within 10 feet of your little miracle baby as nobody should ever say anything of the sort to anyone