Just remembered about this thread and thought I'd update.
At the start of the summer we were offered a friend's pony to loan as her daughter had outgrown her. We'd known this pony for a couple of years and my daughter had ridden her a few times and liked her. I then remembered that there are a couple of fields and stables at the end of an industrial estate next to our house (really hidden away so not many people know of it) and so I went there to see if they had any room. They did - a stable and field for £60 a month. There's no running water (she fills up a tank ever week) or electricity and the stable roof was leaking really badly but it's such a short walk from our house that we decided to go for it.
So, since August we've been loaning this pony and it's been fabulous. DD went to pony club summer camp and loved it. She has a friend in our village who has a pony and they meet up together for hacks or to do some jumping. There's an equestrian centre a 30 min walk away (although last little bit is quite a busy road that makes me nervous) so she's been able to enter competitions. We've been able to borrow a friend's trailer if we need to go further afield and I'm gradually overcoming my fear of towing it!
We've replaced the stable roof so the stable's really cosy now. We bought a solar powered light which is perfectly good. We've got in a routine for turning out & mucking out etc. that's working well. So far it's been a real joy.
Downsides are that the pony has sweet itch and is prone to laminitis so I know I'll have to be careful with her come the spring. I'm planning to do all preventative measures before spring really kicks in and have bought a Snuggyhood sweet itch rug and some sweet itch stuff that I think you have to paint on (need to read the instructions!).
She's great with the farrier, not so great with the dentist (they sedated her to rasp her teeth as she'd been quite difficult with her owner but the vet's planning to half the sedation next time in the hope she'll get used to it). He said her mouth was in a really bad state when her owner's bought her but she's fine now and he said annual checks would be fine. She loads pretty well - sometimes instant, sometimes a bit of faffing around but I think I just need to be quicker with the lunge rope.
Where we're keeping her is ideal in terms of being close to home but it is very run down. I worry about all the fencing which is on its last legs and I'm absolutely useless at electric fencing, there must be a real knack to it. I have been offered another field in the village for free but there's no shelter, water or electricity. Someone said I could buy a temporary field shelter for about £600 which would probably be worth doing as if we moved here I would be saving £60 a month. However, she'd also be on her own and I'm not sure that would be good for her. There are 3 other horses where she is at the moment. She's not in a field with them but they can talk over the fence.
Initially I had been planning to keep her at my friend's house as had set up nice arrangement between her and my DD's riding teacher (as mentioned in my OP). I quickly realised this wouldn't work as could see friend was going to be difficult about it. Also DD's riding teacher has been so unreliable. I'm really glad we managed to sort something out on our own so we're not reliant on anyone's goodwill.
I'm really glad we grabbed the opportunity. I'm not sure DD would still be riding otherwise because I think it would have been hard to go from our previous 'loan' arrangement to having lessons at a riding school.
Anyway, sorry about the essay! Just wanted to update. Can't believe I'm feeling so upbeat about it even though it's winter!