The girl looked irked.

irk: to irritate, to annoy

This word is commonly used by Americans, but most English learners in Japan don't know it. This word is much better than a slang item like "piss(ed) off." I recommend that you learn these words too.

To irritate: to make angry or impatient

ex. Her teasing irritates me.

To annoy: to bother or disturb

ex. Gian's songs always annoy us.

To pester: to trouble or bother again and again

ex. Don't pester me with dumb questions.

Also, it is better to know that mad" is used more often than "angry" in American English.

ex. His insult made me mad. He called me "bitch."

Let's go back to "irk." Below are written by a high school girl. "Even if I wasn't his girlfriend" may be corrected by a picky English teacher, but most Americans speak this way.

According to Annie's Mailbox:

Even if I wasn't his girlfriend, I would still be irked. I don't think he should devote his life to me or anything. I just don't think it's nice to treat people like this way.