Brandi - once they've ruled out all of the nasty possiblilities (and I am hopeful that that's exactly what will happen) see if you can convince your sister to take her to a traditional Chinese medicine doctor. They can do an evaluation and help a lot with symptoms that don't seem to have an explanation in a Western Medicine framework. Especially allergies and weird stuff like this.
Living life like there's no tomorrow.
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2007 Look Dura Ace
2010 Custom Tonic cross with discs, SRAM
2012 Moots YBB 2 x 10 Shimano XTR
2014 Soma B-Side SS