FREEZE drying shouldn't involve lemon at all. The major supplier of freeze-dried strawberries is near me, actually-- and they specialize in berries, and only in berries. A few other fruits, but lemon is definitely not among them.
Here's what I wonder, though-- if her anaphylaxis was very recent, maybe she is just on exceptionally high alert and histamine-sensitive at the moment?
Strawberries ARE pretty good at provoking histamine-based responses, independent of IgE docking.