I'm a brownie leader and I'll try to keep it to the facts. ..
You were offered other brownie units but those weren't convenient. In our district we have parents who would rather be on a wait list for 1 unit than go any of the others with space (even on the same night)
What has the brownie unit said about where you are on the waiting list? They should be able to give an idea when a space will come up
Did you know that the Rainbow section is the only Girlguiding section with mandatory leader/girl ratios in the meeting place? There is a maximum number they can take.
Many rainbow parents resist a move to brownies. It's so hard to find leaders for that age that sometimes you have to be really firm so others can have a go
The rainbow and brownie units are independent units and ones intake policy can be different. 1 of our rainbows talks to parents and the brownie units about a term ahead and knows who is going where, who needs a prod and who might need a term more. The others don't think about it until most of the brownies have offered to others
Girls should only stay past 7 in rainbows /10 in brownies in v v exceptional circumstances. Lots of leaders don't have the conversation early or are scared to lose numbers. The section resources are designed for a specific age and you can see the impact of a delayed transition. Girls who are in guides before 11 tend to stick and with the new program in September they'll need as much time in the age appropriate bit to get a gold award.
It's a unit not class - they are all unpaid volunteers and at this time of the year probably out of pocket and fed up
It's a unit decision as to how waiting lists are managed, all the commissioner can do is check it's explained and consistent within reason. Each of my intake decisions starts with checking all incoming Rainbows. 2 of our 3 rainbow units don't bother to check if we have space then get miffed when I say no because I've already offered and at max capacity. If no word from rainbows from those old enough to join on the waiting list, I normally go with time on the list but I try to balance the age mix.