I'm not a vet, but I'm going to go out on a limb and say if she is "getting RI's over and over" and the husbandry is exactly as you say, she isn't actually getting over the RI at all, it's just getting slightly better and then bad again.
How experienced is your vet with reptiles? Is he running cultures to treat with the correct antibiotic? Is it being given exactly as prescribed?
I could be wrong but that's my best guess. Husbandry seems to be on point. My only other guess is there is something in your home aggravating her, do you use any cleaning chemicals, scent sprays, or something like that which might be bothering her? I guess that leads me to another idea, how often do you clean her enclosure and with what?