It is a big leap, a lot of girls stop at U16 though as women's football is generally on a Sunday morning and it's not good with a hangover - that was my reasoning, as I played women's first team for a year then stopped, couldn't deal with it.
Physically, you get some BIG ladies, and it can be a problem, generally when you play at a high level it's not too much of a problem as if you're in the first team at 16 you're good enough. At grassroots you get tiny 16 year old school girls against MASSIVE women, in every department, so then it's ridiculous.
Another thing is the travel, at Brighton we were in the Premier and most teams were at least 2 hours away, some even three, four or five and doing that on Sunday mornings is too much, but because there's such a big gap in quality between grassroots and Premier, the good teams are in the cities, so you have to travel, the grassroots are in the towns, so closer together.