Bald patch?

A few weeks ago I noticed a bald patch on Scarletts back, she was at the vets anyway for her spay so I mentioned it then. They had a look and said it didnt look like mites or anything and as new fur had started growing there it was probably her moulting (she was moulting quite bad at the time) Anyway they said to keep a close eye on it which I have been doing.

I was spying on them both last night from the kitchen window though (she is back with Trip now) and saw Trip grooming that spot on her back. I have never really noticed him grooming her too much before, he usually just cleans her eyes and I just assumed it was because her mane is so fluffy that he stopped there. Then I mentioned it to my brother and he said he has seen him grooming her back quite a few times when im at work. So now im thinking the bald patch might be from him over grooming her there. Is that something that might happen? And if it is can I do anything about it?

Thanks