My girls prefer a ramp over stairs. Maybe try a ramp, it might be uncomfortable to her little knees.
One way to see if you can get her to try the stairs (if it's not a pain thing) is to put a treat just high enough so she has to put her front paws on the bottom step to get it. Keep putting one there every once in a while until she's confident, then one step higher...
good luck with your little sweetie!