Day cares are what they are. Some are better than others, but, in the long run, it's still a ratio of 4:1 or 8:1 when it comes to care for your child. This means that things are going to happen that some parents are not going to like. I say this becuase my oldest child had one bad experience after another no matter how much research I did on each placement.
In one a child bit her so badly he not only left marks, but drew blood. Keep in mind this was not an isolated episode for the attacker, and certainly not the first time he chose my child to attack. I was very put off when the child was not asked to remain at home until his biting habit could be brought under control...I removed my child instead.
In one home care situation, as a toddler, she was not found climbing the wooden childgate until she tumbled with it and ended up with scrapes and bruising so bad I was afraid of being accused of abusing her in public.
I did have some good experiences with child care and found that the one I liked best, where my child had the least problems, was one that while expensive, did offer the ability for me to check on my child via a website connection to a classroom camera.
I don't know if this helps you, but keep in mind, as bad as what happened is, you could be an unfortunate mom of one of the many children from daycares across the nation (including two where I live) that have closed in the last several years due to molestation charges.
The best you can do is talk to the Day Care administration about your concerns regarding the incident and if you do not like their answers, remove your child and research another placement for her.
I am sorry your child had a bad experience. I know what it's like and how frustrated and powerless to change it, you feel.
Good Luck