Should we ask for gas money?

My husband’s grown daughter is currently recovering from a case of optic neuritis which has rendered her blind in one eye. It could be anywhere from four to twelve weeks before the sight returns to a point where she is able to drive, so in the meantime my husband is driving her back and forth to work every day. He is also picking up her children and delivering them to visitation with their father once a week, gathering them from school (and watching them until she is off work), and taking them to any other events or appointments that might come up. The drive to work is fifteen miles round trip and he’ll be making it for the foreseeable future. We have three teenagers still living at home and money is pretty tight at the moment so I’m looking for input, is it unreasonable to ask her to pitch in for gas money?