C.W.
It sounds like something is rubbing against her back, maybe a tag, or something she sits in or lays in? I have found that bag baum and udder cream (sold at drug stores like CVS) work on almost anything when all else fails. I have used it on the toughest rashes on my kids from infant through childhood and had good results. You can also use Eucerin. Lotrimin is for yeast, and I imagine it would be irritating on a small child. I would counteract it with Eucerin on top of it. Same with a layer of hydrocortisone and Eucerin.