grandaughter's bath times

I say bathtimes what I really mean is "lack of" my gd is 8 months old & has quite a bad rash under her neck which seem to be getting worse although it doesn't seem to bother her.my dl says she trys' to keep it dry & puts cream on & it clears up & then it comes back so anyway i just nod & say ah poor thing....the problem iv'e got is i don't think she washes her that much let alone bath her(baby doesn't like it & screams) so obviously that upsets her(shes a new mum)so i think it's just probably sweat. I just feel sad that she never smells of baby talc but shes a grat mum so don't know how to suggest diplomatically TO WASH HER I haven't mentioned it to my son i know he does express surprise sometimes & has said occasionally she hasn't had a bath for a few days has she?to his wife I just find it very odd you would think shed enjoy that part of having a baby any suggestions welcome i get really upset about it privately but feel ashamed & can't talk about it to anyone through my love for dl