[Doc Holliday]

If your school has a really good AD they normally have coaches of the athletic teams create a written policy, then in turn the cheerleading sponsors should have one as well. These policies normally are presented to the principal and site base. However not all schools adhere to that, most programs are ran with aet rules some are lax and the coach of a sport or a sponsor can do as they please.

If the student in question was given a set of rules, and they signed off that they would follow them then that doesnt all ways mean that they can't comeback.
I know of it happening this year, where a girl quit and the principal happened to be there, he sided with the student and asked her to reconsider her decision, she didn't ask to put back on. The principal wento the sponsor and informed her that the girls would cheer the rest of the season.

But as a Coach I would tell you that if you quit, you quit, and you are welcome to come out next year.
I would also tell you that where I used to work we had a rule that if you quit as a freshmen in certain sports and clubs you could not come out for one year, which meant you had to lay out till you were a junior.

With your comments about the sponsor being unfair and playing favorite, to be honest I wouldn't let them come back because its very apparent you or they are not going to be happy.

I would say go to sitebase and the principal, you may get the rules changed you may not, but who will know till you try.