I am taking "on the bit" as a term for some collection alright? :)
So first of all...if your horse slows down while "on the bit" then when you ask her to move more forward she "gets off the bit" or in my words hollows...then you can, "only keep it for a few steps to a long side of the ring." there that is a tell-tale sign she isn't truly through or connected over her back. Perhaps you should focus a bit more on getting this horse a bit more honestly through...not just in a pretty head-set. But easier said then done;)
As for the bending: it sounds like she is really stiff. Doing some flexing work, on circles and on the rail, are the best things to do. Try some over-bending, some counter-flexion, just get her to release her neck. She will never be to truly collect if her neck is tense....her back is probably tense as well. Do some long and low stretchy circles as well to flex her neck longitudinally as well as the lateral flexion stuff. Until she is free with her neck, don't try to get her "on the bit." This might mean several rides where you don't do anything but flexing and some relaxing exercises.
Good luck...hope it helps a wee bit!
Originally Posted by Ponypwnage
I recently began riding this horse after her main rider went away to college. It is rather difficult to bend her unless she is on the bit. I can bend her without her being on the bit, its just harder so I try to have her on the bit when we are working on something. The trouble is when I do get her on the bit, I can only keep it for a few steps to a long side of the ring. She is normally a very forward horse but when she is on the bit she will slow down and when I ask her to step it up, she will come off the bit. I have an instructor, but I am only taking group lessons so she is unable to watch me all the time. So can I have some help please?