say i overgamed a girl who showed initial sexual interest. teased her too much, kept her waiting too long or whatever and she became unresponsive. i backed off for a while and pinged her with a low-investment text message a month later. she replied with: "you're cute but you fool around too much. i'm not into that."

is this salvageable?

I would say its probably unsalvageable, the girl has formed this opinion of you and clearly she doesnt like the image involved with it. The only way I can see you picking up from this is to protest that you're not a "player" and tell her the opposite of what she thinks. It would be a pretty AFC move as you're compromising yourself to get her thinking that you're not that bad. But I can only see that as an option, while some girls will like thinking of a guy as a player, and the Alpha image it portrays, this girl isn't one of them and has formed her opinion, hard to reverse that without pandering to her assumptions.

Just my opinion but see it as a lost cause, others might have a different take though!

In past experiences with this i usually flip their frame around on them (her frame on you is your a player , your not serious ) as u stated shes not looking for that so flip it round and Frame her ass !
say something like " your all alike , you always expect me to be the fun guy , have you ever gave me the chance too be serious............ buy me coffee ........... let me prove you wrong "
( your jumping through her hoop but shes also jumping through your hoop so its cool )
From then on either A) game her as usual but by building rapport and breaking it only!
or
B) run some NLP rhythms on her.

At the end of the day , if she cant handle you tough shit and let her know that !