The 7 year old chugger in our midst

Righto, this post is going to be a bit odd (read hypocritical) bearing in mind the last one I just uploaded but I need to get it off my chest.
Since my kid started primary school there have been quite a few times where we as parents are asked to donate money - cake sales, spring/christmas/summer fairs, magicians coming in, kids going off to plays, kids going off to museums, kids reading aloud, kids dressing up, kids growing flowers. There are even sponsorship forms for her to get more people roped in which is hard as we do not have any close friends or relatives in the town. The requests are endless. This year seems to have been particularly bad as there has been one request after another for donations. The final straw was yesterday when we found a letter in her bag asking for £6 for a Roman day - a guy is going to come in dressed like a Roman and show the kids a lot about Romans.
I am so glad we only have one child as if we had more, there is no way we could afford all these constant requests for money. And when at the teacher evening last night, we asked kiddo's teacher what happens to the kids whose parents don't pay, the teacher had no response. Which implies that they expect all the parents to pay. I know for a fact that some of the parents are struggling financially and this is pressure that they will not need. I also know it's these parents who will try their hardest to find the money.
Whilst I don't want my daughter to miss out on any activities I'm not really sure that turning her into a chugger is teaching her anything about charitable giving. For e.g. kiddo now hates all Cancer charities except McMillan as that's the one the school supports. We have tried to make her understand that is a poor view but she's adamant that that charity is the best one.
Up until now the dosh has come out of our pockets. So we are now going to start telling her the donations should come partly from her pocket money - so the next time she brings home a letter asking for a donation she will also have to cough up (and yes, I know that's ultimately us paying as we are the ones supplying the dosh but there is a lesson to be learnt here dammit). Hopefully that will open up a discussion on when it's best to give, and when it's best to just say no.