I would suggest that you monitor her bathroom habits by letting her go and wait until she leaves the bathroom and go in right away after she gets done. If her pop is in the trash can call her out on it and tell her to stop doing it and use the toilet. If that doesn't work, remove the trash can, if she goes and finds that the trash can is gone she will go into the toilet. I'd do it for a month and if that gets her to stop then she has learned her lesson, if not and it's on the floor or elsewhere I'd punish her until she learns to use the bathroom correctly. If there's still a problem I'd would get her some professional help.
Having the same issue with my 10 year old daughter, she also pees on her floor...