2 year old girl has bald patches and itchy skin

[Sharp]

My 2+ year old rat sesame has always had a bald tummy but lately she has been balding and scratching more, none of the rats in her cage have the same issue and do not scratch any more than the usual itch, she has wounds that have not healed over time becaus she keeps scratching them. My boyfriend thinks she has something genetic that causes her to have dry skin and I believe she had babies before I got her but I'm sad to see her groom so much and hurt herself, any ideas?

 

[Sharp]

My 2+ year old rat sesame has always had a bald tummy but lately she has been balding and scratching more, none of the rats in her cage have the same issue and do not scratch any more than the usual itch, she has wounds that have not healed over time becaus she keeps scratching them. My boyfriend thinks she has something genetic that causes her to have dry skin and I believe she had babies before I got her but I'm sad to see her groom so much and hurt herself, any ideas?

All of my rats have been treated with invermectin so I don't think it's mites.