A.,
I think the best idea is to not make a big deal about this. When you catch her doing it, sit her down and change subject, if she inquires about it...answer swiftly. I am E.'s daughter(with 3 children). It is normal for some girls to think peeing like a boy is cool. If you don't draw too much attention, it will pass. So, every time you notice her go to the restroom, just sit her down and begin talking about something that interests her. The phase will pass as many others do. I don't think the preschool thing is bad; almost all preschools are like this, and generally teachers can be made aware if this is an issue for your child. Remember she is quite smart! She is just trying something new and notices your reaction.
E.:)