K.B.
I would ask how long she worked for them - shows consistency or lack there of.
What are her strengths - so you can know where she's good
What are her weaknesses - good to catch "pretend referals" for they never have ANY negatives. Also a good way to know what the challenges would be ex. Always late, or not great with a baby etc
Would they refer her to a friend or family member. I love this one cos then you really know how confident they were of her abilities altho I doubt anyone would give you a referral of someone who wouldn't give them a good grade ;)
Good luck!