When does the baby chub slim down?

Rαȥȥყ

My daughter is 7 months and she's a little chubber ❤️😍 The issue is, she doesn't have much of a neck so we are really struggling with trying to keep her neck folds dry and clean. It is reallllly hard to get in there and she screams bloody murder when I try. I am constantly cleaning, drying and using babypowder/diaper rash cream but it's still always red. Just curious when chubbier babies like her start getting a neck?