My question involves child support in the State of: SC

My fiance and his ex-girlfriend, who was an illegal mexican, had a child together. When they split up, they went to Court in SC. The judge awarded 6 months of custody to the mother and 6 months of custody to my fiance. After that time, they were to go back to court and joint custody was to be granted. The judge also told the mother that she could not leave the state of SC.

Without notice, the mother took the child and ran off to Texas. My fiance has been trying desperately to find his daughter and the mother has made no attempt to contact him, until last month. My fiance was served papers that the mother was suing for child support.

Is this legal for an illegal immigrant to sue for child support? How does he get his daughter back? We want full custody of the child.