MrsR, if they are a genuine rescue they won't mind you being concerned about their animal's welfare. But they do deserve a chance to explain.
Did you ask if the foals were new arrivals under vet supervision?
Horses and ponies are notoriously slow to recover from neglect and often look really rough for months after being removed from bad situations. Overgrown hooves sometimes need to be left while medication deals with infection, for example.
Was the lady's dog a recent adoption who arrived pregnant?
Was she just telling you it was her dog because she didn't want you to ask about adopting it?
About not being allowed to see the kittens except through a window, well that would seem a standard hygene precaution to me. Especially if there's flu or ringworm going around. In fact, I can't think of a single rescue I've dealt with that allows folks to handle kittens without first making a special request. And if a litter of kittens are all sharing one tray it can look rank within half an hour of being changed. (That's why rescue gets through so much litter!
)
I'm not saying what you saw wasn't good practice and wasn't distressing but sometimes at first sight, rescues can seem bleak places. Very often they are! But they are often, quite literally, the last place these animals are welcome and the alternative is PTS.
What you have to balance is whether these animals are being abused or are merely being cared for by folks struggling with poor resources and poor knowledge of animal husbandry. The RSPCA will be best to judge that.
As Christine says, they are collectors out there and they need to be educated but they also need support and to be encouraged into better regimes. Rarely this kind of set-up is intended to abuse, and it usually starts by the owners heart felt desire to help animals and make a difference that was executed poorly and under resourced.