Being a semi-professional photographer, I took a picture of my friend and post processed it for free. She then edited the picture without my permission and posted it on her social media so I got angry at her.
Why did you postprocess the picture for free?
I wanted to be nice.
That was kind of you to process them without charge and your current frustration is understandable. The edits alter your work and are no longer a true representation.
I have ignored her multiple times. I think I should just let the situation go.
You can let the situation go if you want, but removing the post is fine, too. She did it without your permission when it was your property, so it is up to you what you do.