my own dd went up to secondary last year, and my feeling has been that this is a time when you really need to start letting them feel grown up and responsible, at the same time as making it clear that you expect them to take responsible decisions where it really matters
so to me- attending school, working hard in lessons and doing her homework would be pretty non-negotiable, though I do make it clear that I expect her to be able to take responsibility for that herself
any out-of-school activities I would expect her to have much more of a say in
I didn't make dd join the g&t club even in junior school (YR 4 I think it was), because she made a good case for the alternative, pointing out that she did not want to choose her friends according to whether they were gifted or not
if I understand it rightly, you feel she ought to be doing one of these workshops in order to become part of her new school
first of all, I would do a bit of a poll among other new mums to find out how many of them are actually doing it=how essential it is
then I would think about whether your finances are too tight to allow your dd to have a say in this
if so, explain this to her (I find my dd is always quite accepting of financial constraints, as long as we discuss things with her as with an adult)
if financial considerations are not overwhelmingly important, then I would try to weight this against allowing your dd a say in the decision
I would think it very likely that she is anxious about the social side of secondary and does not want to be singled out from the start