How do i tell mum she is hurting my feelings?

My mum delivered a stillborn at 23 weeks last september. She has been trying to have a baby for 6 years and the event was heartbreaking for the whole family, she never seeked professional help and has just moved on to talk constantly about her next baby. Through it all I was her main support as her husband fell apart and the rest of the family do not approve of her trying again. In january my husband and i discovered that after a year of trying to concieve for 12 months we were finally pregnant. i don't parade around my mum but i also don't treat my pregnancy as taboo, now i am getting a lot of hostility from mum, if the baby is mentioned she gets nasty and says i am fat (although i have only gained 3 kgs ) or that i shouldn't be having another baby because i have 2 already (even though i am 1 of 6 children) and she hits my belly as a joke but she really bashes it and it hurts. i don't want to hurt her but i feel like if i don't say something my mere presence is hurting her.