Multi-person finger prints?

First, I have searched for this but came up with only instructions and tips on how to set it up, not my particular question (but it may be how I'm asking it!!). My question is whether anyone knows why the finger print scanner would accept my prints quickly and easily (meaning I don't have reason to think the scanner is faulty), but not work on my wife's at all. I'd like her to be able to easily unlock my 6P in the case of an emergency but it will only record her 1st print, then fault out on all subsequent attempts - on either index finger. It seems to accept any of my fingers, but none of hers. Can the scanner be slightly defective so only more prominent ridges are picked up (I'm talking waaay over my head here, just throwing out questions).


Any thoughts would be appreciated.


Thanks,