Just keep the charger in your car and the next time you see her you can give it to her. At this point, it is up to her to make an effort to get it back but you could remind her about it next time you see her in person.
Alternatively, if you did not care about hooking up with her again you could...
Drop by her apartment with the charger when you know she isn't there but her roommate is.
Bang her roommate.