Babysitting a 71/2 month old and parents not responding to problems.?

I am babysitting a 7 1/2 month old who obviously has plagiocephaly(flat head syndrome) as well as is very fussy. I have told the parents about both issues. Unfortunately the parents think that it will fix itself and they say that she is not as fussy when she is at home with them. I am not sure of what to do if anything. I understand that she is not my child, but I feel bad for her (since they are not doing anything to solve the problem). And in a way, I feel a little insulted when they say that she is not fussy at home. I have 2 other children and neither were overly fussy. I have tried everything that I did with my little ones when she gets fussy, but nothing helps. I am babysitting her because her parents asked me to(since we are friends), not because I was soliciting a caregiver job. Should I continue to watch her and just say nothing more? Or should I stop watching her(it breaks my heart to see nothing being done)?