That looks like she has had some old shed stuck to it which has constricted the tail and caused the damage when it was removed. Basically it is exposed flesh and bone.

When they shed it is important not to leave any stuck shed that completely encircles the body.

Stick to a non-particulate substrate ( which you already have ) and apply either some neosporin ( the type without pain relief ) or some of that silver sulphadine paste that I always get the name wrong - some one will be along shortly who remembers the name of it I'm sure.

Also you mention day time temps - there is no reason to give them a night time drop at that size.