Well I absolutely hate it when girls do that, because I love making out and so far every girl I've been with says I'm a great kisser and I think so as well. But I can't stand it when a girl doesn't open mouth kiss so I do a few thing to try to get her to do it.
When she doesn't want to make out I simply back off , tough her face gently and then kiss her cheek and move slowly down to the neck and then I basically french kiss her neck. Then I increase the pace a bit and move up to her cheek and to the side all the way to her ear.
(This is where you will really turn her on) You kiss and suck on her earlobe and lick just slightly inside of her ear but do it gently and it will give her the chills. Kiss her ear and she will hear the sucking of your lips right on her ear.
After that I usually don't have any problem with open mouth kissing her because she is so turned on and I turn up the pace a little bit while kissing. It escalates very well too.
This italian girl I've been sleeping with goes absolutely nuts and that's all it takes for her to get insanely turned on.