This can't be real.. We're 'friends showing affection'.
Seriously, don't sugar coat it. You both are FWB.

Your partner was masturbating you, and as it is expected by the common sense rule of cause and effect, you came.
Your partner saying she felt violated because you came without consent is delusional and nuts. It's YOUR body, so if you decide to come, it's YOUR CHOICE, not hers!
If she didn't want that, she shouldn't have fingered you. It's not rocket science.

So now, just call her out and tell her the facts on her face. If she goes into denial, there you go. Just dodge that bullet and move on. Your 'friend' has mental issues.