I think that girls tend to fall into two categories.
The shy pisser is probably not used to pissing in the bushes. She's probably been out all day and put off going for a wee until she can't wait. She usually goes either alone or with a good friend, or possibly boyfriend, and tries to hide very well and double check she can't be seen, before timidly squatting down.
The confident outside pisser is quite free and happy to piss outside, and doesn't wait until she's desperate, and will confidently walk into the bushes and squat, probably not being too concerned about being seen.
Another time