I would let her know personally. Yeah maybe she'll chew you out, or just not respond (I've had both), but she may appreciate that you took the time to explain to her once another dude comes around and decides to pump and dump.
Women will pretend like your words don't mean shyt, but in my experience, they'll go home and replay the things you've said in their head. Save all your texts and reread them from time to time. But most importantly, you used your voice to speak your opinion and didn't just keep quiet.
However, if all you have in your head is mean spirited shyt that is ego based then yeah you may want to just ghost.