A friend just replied to a text I'd sent her hours earlier with the following:

In the interest of open communication, I'm kind of hurt right now and not in the best state of mind for texting.

I think she's probably upset because she found out that I drunkenly made out with a mutual (male) friend. This mutual friend is much closer to the texter than to me, but the two of them have never come close to hooking up or dating. Still, I feel like she has this proprietary thing with him, even though she has repeatedly insisted that she does not find him attractive or have any feelings for him beyond friendship.

I don't really feel guilty for kissing him, but I am sorry that she's hurt. Should I text her back an apology or leave her alone until she cools off?