Make sure rooms are well ventilated,there are certain chemicals you should stay clear from during painting,because of the fumes.
It is completely safe to paint during pregnancy as long as it is with water based paints and not oil based and most paint are water based. Primers are usually the ones that are oil based. She can ask he DR about it and they will tell her the same thing. I am sure she is fine.
It can and the fumes can casue harm to the developing brain and other parts as well as chemical effects and oxygen. It is nto good to be around cleaners or paint. THere are lots of Benjamin MOore paints that are made with milk or natural things that are safe. ALso natural cleaners to use. You have less oxygen to your brain during pregnancy as the blood flows goes more to the uterus is why we get more forgetful. SO you do not want any less oxygen to you or the baby. well that is the facts. But to late now I guess don't let her worry though just tell her the things that is bad and she can try not to again.