Thanks for responding to my post.

She actually is a good friend and she is struggling with clinical psych issues. She generally is a good person to talk to except when something seemingly neutral upsets her. She is aware than she does take things a bit too personally and is actively working on it.
I figure the best thing for me is to add breathing space to our friendship when I become frustrated and that is what I've been trying out since I posted. I feel like the "eggshells" thing may have been an overstatement since it's only when she gets upset that that pops into my head and I get wary.