To right she should not get involved, she should remain impartial for her grandchild's sake. no matter how bad her daughter has behaved
you are in the european union remember, of course you can make her pay, well at least a court order to pay will happen wether or not she will pay is a different matter, and you will have to keep going back to court till you get a court order to take direct from her wages.
But do you really want your daughter to see her father stressed out pursuing her mum through the courts for a few quid. and as you are living in spain it will cost you a fortune, as the hearing will be held in the country of your residence. no free lawyers in spain.