My daughter, 15, would have done the exact same thing. She is extremely sensitive, especially about animals. A few recent examples-
I've been trying in vain to find a luau, (we are going to Hawaii over Christmas), that does NOT make the cooked pig a part of the ceremony, but no luck. She would never attend such a ceremony.
We ate at a restaurant the other night and my husband ordered steak. When it was brought to the table, it had a little plastic cow pick stuck in it. DD15 got tears in her eyes.
We were driving down the highway and there was a big ant crawling on the floor by her feet. She wanted me to pull over so she could release it into the woods.
Just thinking about an animal getting hurt can cause her to cry. She also will get upset if she sees someone who looks sad, (a homeless person, or someone who just looks a little different). A few months ago, I remember we were in a store waiting in line and I looked at her and she was tearing up. When we got outside I asked her what was the matter. Seems there was an elderly gentleman walking around wheeling an oxygen tank with him. She was so upset and felt so bad for him.
She certainly wears her heart on her sleeve. So, I know exactly what you are talking about! Hope your daughter is feeling better!