Clearly, I don't have a vagina but a well noted guide on Kindle called "How to Make A Girl Squirt" written by a female. Said that most women who think they can't usually stop themselves short during stimulation because it feels the same as peeing and when they are about to they collapse their muscles to stop it. So my suggestion. Just let the flow explode out.
The other recommendations were throwing a towel in the dryer right before wrapping yourself, out of the bath, so the towel is warm/hot and of course a clear/relaxed mind. You ladies are so emotional!
(I mean that in the most sarcastic, true, but I am just playing way, possible.)
As a guy, nothing has excited me more during sex than a squirter. It's also very hot to watch.