I asked because I thought she might have an allergic condition my cat
has--EGC--but if she has no bumps, she doesn't.

Since you say she is nervous, she is likely grooming the hair away out of
anxiety. I know this is going to sound stupid, but try to figure out what is
bothering her and fix it.

When my girl came to live with us, she had a naked bikini area. :) It stayed
naked and pink until about a year ago, which is when I figured out that she
had been nervously grooming the place ever since her spay.

I found out when hair began disappearing on her flank. The only thing that
had changed was that our other cat, who was here when she got here, was
coming up into the guest room where my nervous girl liked to sleep, and
getting on that bed. The latter cat was doing that because she had somehow
gotten more attached to me and wanted to be with me, upstairs where the
guest room is. I began spending time with that cat all the way down on the
first level, she stopped coming up into Gracie's turf, and Gracie's fur grew
back on her flank! As she grew happier her bikini area began growing in, and
now she has that gorgeous thick vanilla-and-spots thing that tabbies have
going on. :) I kiss her belly every night, quick like before she can start
rabbit-kicking my head!