Only read the first page of replies.
I agree with other posters the this is still the owner's horse. I get it can be annoying having someone breath down your neck while leasing, but with a fancy dressage horse I'd be quite worried if the owner wasn't breathing down your neck about things.
I own a nice hunter/eq mare. Right now she's doing A/AA circuit at the 3'3"-3'6" levels. She has potential to move up a fair amount from there as well. She is on lease for 10 months while I am in school and will come home August or September of 2015. The lease is a free lease off property 3-4 hours away. My other mare is still with me, I just simply didn't have time for two while in school. I have part-leased out said mare before (on property, 2-3 days per week). I spell out my contracts VERY thoroughly - like BugZapper I need to approve absolutely anything used on her. Both my mares are my babies, but I am especially picky with a mare at this current level - she has way too much potential to be wasted and/or ruined. I cover all her expenses while part-leased on property and the leaser is to pay a portion of the board to myself, as well as lesson/show/clinic fees. While she is being free leased off property currently they cover all her expenses, minus any serious non-routine vet care (obviously this is spelled out much more in detail in contract regarding who pays how much and in what cases in regards to such events as colic, needing stitches, yadda yadda).
Bottom line - it's HER horse. And by the sounds of it one she has a fair amount of time/money invested in. I can see where she's coming from.