trouble with red marks on legs

We have been cloth diapering my 7.5 month old since she was about 3 months old. We use the best bottoms diaper system (an AI2, liners that snap into shell). She has rather sensitive skin and does get diaper rash every now and then. We've been using coconut oil on it which works most of the time. However, my problem is with an awful red marks she gets, not in the actual diaper area but on her thighs where the leg gussets are. I guess I'm not even sure if it's techniqually diaper rash or something else. The skin on her thighs get very red, hot sometimes swollen looking and eventually gets kind of chapped looking and eventually begins to peel. I have tried everything I can think of... loosening the diaper (to the point where it often leaks), generously coating her legs as well as her diaper area with the coconut oil, changing her frequently, never using the same shell twice in a row, stripping the diapers 100 ways to sunday... nothing seems to help. The only thing that clears it up is switching to disposables for a while, but the rash always comes back within days of switching ther back to cloth so she has now been in disposables for a couple weeks bc I feel bad about continuing to put her in the cloth ones and "giving" her a rash. Has anyone encountered something similar and/or have suggestions for what may be going on? I've considered an allergy to what ever kind of elastic is in the gussets but the elastic is covered in cloth so I don't see how that would be an issue...

My Amelia got terrible red marks on her legs from the elastic on motherease airflow covers (even when they were super loose) but does fine with best bottoms... Maybe try a different brand of covers?

If wool seems too complicated (I know it did to me at first) you could try a fleece cover too, those are machine washable and look to be much more gentle on the thighs... 

If you want to keep using your best bottom snap in inserts you could try another PUL cover like a flip that has the flaps to hold the insert in place.  I use my best bottom inserts to stuff my pockets sometimes as well.