Very simply, sometimes instead of only rubbing my girlfriend’s clitoris during touching, I sometimes gently tap the hood and the tip of the clitoris.
This is much more effective when she is already aroused, usually through breast stimulation.
Also, when tapping, I like to use her secretions to gove some lubrication. This helps the tip of my finger slide around a bit as it taps.
Depending on her sensitivity, you will want to be careful not to tap too hard.
While I don’t have this problem, if she takes a while to come through licking her clitoris, you maybe be able to speed up her oral orgasm if you prep her through this tapping method.
Also try inserting a finger and lightly tapping the g-spot while another finger taps her clitoris.