I hope you don't mind but I've moved this to where it's more likely to be seen.
Is this new behaviour? If so I would be looking for some reason why she's started doing it.
Training wise I'd try to get a helper on the ground to begin with. Stand the helper where the horse's head will be and ask them to just stand there, not hold the horse. If you don't have a problem with treats then a pocketful of nuts or similar can be useful. Lead the horse up to the mounting block, and if safe walk backwards in front of them and stop every couple of steps, it gets them thinking of halt and also puts you in a good position to line them up correctly. Lead them up to the helper, halt and praise with the helper giving a couple of nuts. I find it helps if you have the block positioned so you line up the horse and then go up steps by the horse's head, many horses don't like a rider going up steps before they are at the block.
When getting on the mounting block the rider has the reins, not the handler. Handler's job is to provide a visual block and keep the horse relaxed. Make sure not to tighten the inside rein as that will turn the horse into the block and swing the quarters away -you don't want to mount over the head! At this point the rider needs to calmly get on with it, not faff or be slow. Make sure not to dig the horse in the ribs with your toe, kick it on the rump, pull on the saddle, or crash down into the saddle. Get on and praise, get the handler to give some treats and praise too. Personally I like the rider to lean forward and give a particularly tasty treat because then they learn to wait for that one. Feet quickly but carefully in stirrups and then ask to walk away, to begin with don't make a point of standing too long just get the mounting sorted, you can work on waiting around later.
Obviously the person on the ground has to be sensible and aware, although a visual block they don't want to put themselves in a situation where they may be run over! Sometimes with a very bargey horse a rider on a bigger horse stood diagonally across the front of them is a better bet.
Repeat and repeat and repeat, with the handler gradually moving to the side. If the horse moves away just calmly turn him away from the block and start again. To begin with allow yourself plenty of time, this isn't a lesson to be rushed.