It's normal while she is nursing, she is just wanting to protect her litter. Being a PEW doesn't help either as their vision is even more reduced than a normal rat. Normal rats can see about 4-6" in front of their face and it's not very focused. Pink eyed rats see even less, so it's understandable that they can be easily startled and may bite or "taste" first before calming down.

I don't tolerate biting AFTER they've weaned their litter. If it continues while they are resting and don't have babies around, then they are retired. I don't tolerate biting or nipping any other times.