What I want to know is How hard is it to get a standing back tuck? Is this something that I could help her on in practice if I talk with the gymnastics instructor and get some instructions on how to help her?
If you went to her gym Coach and asked how to help her I think you would definitely be fine. However, you would need to get as much information as possible. Not just, "well this is how a standing tuck is done". There are so many things that can go wrong in gymnastics (as well as cheer - or any sport for that matter) when new things are being learned. You would need to have the gym Coach explain to you the typical problems/habits that occur when learning a standing tuck and what to do as a spot in those situations. It really is not that difficult to spot tumbling passes up to layouts. Fulls is where it gets a bit tricky in my opinion. However, just like in stunting, there are many things you as a Coach/Mom spotting your daughter need to be aware and prepared for. Seeing as how she already has a tuck in a running pass, that might make the standing tuck be a bit easier to get. But, it could also make it harder. It really just depends on your daughter. Tumbling is so subjective for each kid because of the mental standpoint that is involved. For example, I could do a tuck long before I could do a back-handspring and I was a gymnast. I just didn't like putting my hands down because it scared me.

How silly, I know!