My 5months old daughter is always throwing up her formula when I add rice to it! Can she be allergic to it?

Why are you putting rice in her bottle? At five months all she needs is formula.
It may be too heavy for her.She is getting too full from the rice and it is making her vomit.
Cut out the rice and see if the vomiting stops.
Rice is very passive,I doubt it is an allergen but it may be making her too full.

This might sound dumb,but is she throwing up when you don't add rice?

If not,don't add rice.