Your mom needs to knock it off, and if she doesn't you may need to set boundaries. No one - absolutely no one - should comment on how someone is gaining weight while pregnant. If I'm to be honest, I think even some healthcare providers cross a line they shouldn't cross. I was harassed by my healthcare providers over my weight gain during both pregnancies and with my son I literally gained only what they wanted me to. I just gained it "too fast" (ugh). He was TEN POUNDS and his placenta was HUGE. So literally everything I gained was him, placenta, and amniotic fluid and blood.
I had hypermesis with my daughter, and gained weight fast once it eased just a little bit. Did I lose the weight easily? No. Did breastfeeding help me lose weight? No. (It doesn't for everyone...) But none of that matters. What matters is a healthy pregnancy and the baby. I know it's hard to accept this, but at the end of the day unless your weight gain is caused by something like gestational diabetes or preeclampsia, it is perfectly okay.
I know doctors like to say that 25 lb thing, but the real range is like 15 to 50 lbs being normal weight gain. So, relax and take it easy. I'm glad you're feeling well enough to eat. Hyperemesis sucks.