Was she getting these since she started using grips or did it start after she began tightening them? What color are the marks? Red or purple-ly? If they are reddish, she likely doesn't have enough proper padding under her grips to prevent the digging, particularly at the wrist which can be a problem spot for the grips rubbing. Try to get the padding (neoprene or the sweat bands) to ride up onto the palm a little more to protect that area. Dd had this problem initially but she got used to it and so did her hands. They toughened up on their own. However, if it's purple-ly, she might be cutting off circulation. Talk to her coach about it and tell dd that she needs to loosen the grips a little. What is she doing on bars that is making her want to tighten them? A lot of girls tend to do this when they are working on a new skill -just to be sure the grips don't fall off. The problem is they get used to it and then the next time they try to make them even tighter. If she is getting indentations and bruising color, she could be pitting enough pressure to be damaging her nerves as well. Does she complain of tingling, not being able to feel temperature or pressure? If she doesn't listen to you or the coach about loosening it I would make an appt for the Dr after one of her bar rotations so that he/she can see it first hand and talk to your dd. And just because it doesn't hurt, doesn't mean its not bruising.
Also, I would be weary of anyone but the manufacturer cutting down grips. I am sure the coach thinks he/she knows what she is doing but its not a good idea as it can change the integrity of the leather. Going with a different brand with smaller palms (pixies) or waiting until she is larger probably is the way to go.