So, 8.30 until 5.55, for example?
If so, and it's not every day, that sounds completely normal.
How long is the lunch break?
Is there a short morning break? A shirt break at the end of the day, before the after school activities?
My daughter's school day was 8.30 until 5.15 every day.
On days with her scholarship activity, she finished at 6.30pm.
It's not like they're engaged in the same activity all day.
If it's a private school, there are no legal guidelines for timetabling (except possibly a minimum number of learning hours?)
Is your daughter's school also a boarding school, even if she doesn't board.
I'm afraid that your options are to turn down the scholarship, if you won't want her to do these activities, or to go with it.
Complaining will make absolutely no difference, I suspect!