Hello, obviously it is different for every child but I would definitely expect an 'average' 8 year old who has been riding for 2 years to be able to ride off lead rein and canter by now, most would also be able to do things like trot without stirrups and pop a small jump. But more important than what she can or can't do, she should be making progress, should know what she needs to work on to improve her riding and should be enjoying herself, it sounds like her current set up isn't doing any of this!
I wouldn't blame Pony Club per se, but each club (especially the ones for children without their own pony) runs things differently and in some places, the PC lessons are quite a short and basic session, and the children are expected to have private or group lessons separately in order to actually learn and progress. The PC sessions are just there for some extra riding time, fun and games or a chance to demonstrate what they can already do to earn badges. I'm not saying the centres/clubs that run things this way are doing it wrong, as often the PC sessions are much cheaper than a normal lesson, have to cater for a mixed ability group and/or contain an element of stable management alongside the ridden session so don't have a huge opportunity for individual teaching.
But really if this is the case at your PC someone should have explained this to you rather than just keep your DD at a very basic level for 2 years, many DC would be completely put off by now, so it is not good teaching practice.
I would either speak to whoever the 'lead' instructor at the PC centre is about how your DD can progress (perhaps through booking a course of private lessons) or go elsewhere. If you do the latter by all means choose somewhere that also offers Pony Club but don't be bound by that. When you speak to a new school, I would simply explain she's currently a beginner and keen to progress and ask them what they recommend, rather than saying straight away she wants to do pony club as this could confuse them. E.g. at the stables I ride at, they wouldn't recommend children of her age join the PC sessions until they can at least confidently walk and trot off the lead rein, so they would probably say she should have private lessons or ride in a small group of other novice children until she's at that standard, and then join the PC (but it may work differently elsewhere so keep an open mind!).
Good luck!