Hi Michael, what a gorgeous girl you've got there! Sorry to hear about her renal issues.
When you mix a new food in with her Hi Tor, how much are you adding? I would try again, but with even less. Like 1/2 a tsp. Blend it thoroughly, and after she's been eating that for a few days, go up to a full tsp. Then a tsp and a half, and so on..... It's not unusual for cats to be suspicious of different foods, so the key is to go extremely slowly and allow them plenty of time to get used the smell, taste and texture. Not sure if you've tried this, but if she has a favourite treat or type of kibble, you can pulverize a few pieces and sprinkle it on top of whatever it is you want her to eat. Also, don't limit yourself to prescription foods, which tend to be junk anyway (don't know much about Hi Tor so I can't comment on that). Look for lower phosphorus commercial products from these lists:
http://www.felinediabetes.com/diabetic-cat-diets.htm
http://www.felinecrf.org/which_foods.htm#US_food
Perhaps something on there will be more appealing to Mrs. Kitty. After all, the most important thing is that she eat.
Good luck!
