My daughter is 18 and has a baby girl. Her mother asked her to leave the house about a month before her 18 b-day. I have been paying her mother child support. The divorce decree? Does state that I am only obligated to do so until she turns 18. My question is can I ask for support from the mother since my daughter is still attending college full time?

Here is a link that may be of assistance to you.
Post-majority child support collection laws

What state is this in ? Makes all the difference.