Should I harass this poor girl?
That does not sound good. Why are you going to harass her?
She said something to me and I don't want to let her irritate me so much.
You may be irritated, but that is never a justification to be a bully or harass someone. That girl doesn't know that she may have annoyed you, so it's not fair to her at all that you want to make her life hell.
But she said something to me. I don't care if anyone is in a bad place, they are going to pay for irritating me.
But maybe she didn't mean it or she didn't know how it will affect you. You shouldn't bully her just because you are irritated.