without looking at the lock, my first guess is that the lock is older, and your wife pulling her key out managed to dislodge some gunk that was keeping it operating smoothly. another possibility is that she didn't manage to fully relock/reset the lock when she took her key out (again due to age related wear) so that your key couldn't get past a pin that was still set or caught on the body.
if it's a newer lock, odds are gunk got in on one of your keys and affected a similar result. (as stated by booka, bump keys are not typically a burglars tool of choice, unless you're a locksmith, or a locksporter, it's very hard to argue that it's not a burglary tool, which significantly bumps up jail time.)
you've got a few choices:
a-do nothing, see if it happens again. (don't do this unless you've another door to get in)
b-squirt in a little lock graphite and see if it happens again (see a)
c-spray the holy monkey love out of the lock with some brake cleaner, (or contact cleaner, anything that won't leave ANY residue, wd40 is BAD unless you intend to lube it monthly) and see what comes out.
d-take the lock core out and (c) (easier on your door)
e-bring the lock in on wed and i can take a gander, see if it's been abused, if there's a lot of wear, etc. (bring along everything, including anything that falls out)
f-buy me a guinness or six and i'll swing over and see what's what
g-hire a lockie to check it out for you (i recommend central lock and safe)