Also, most kinders have 'open' toilets meaning they dont have doors. Ive never really had a problem with this and think it makes it easier for the staff to help the kids if they need it. It also allows the staff to supervise without butting in if the child doesnt want any help, or if the child is mucking around....
If you are concerned you can speak to the teachers and they will make a note to keep an eye on her. More than likely she will be fine to go on her own.

PS- I am loving my 2.5 hrs to myself on Fridays!!! Im sure you will too