An accent!?

Ruby has suddenly developed an accent.

Only one sound is affected: short a (as in sad), and she draws it out like a southerner and says things like hay-ah-ppy (for happy) and cay-ant (for can’t).  We’re mystified as to where this came from since we don’t know anyone she talks to that has such an accent. Asking her hasn’t shed any light on it either. Our own speech is a fairly neutral northwestern U.S. accent, with a Canadian seasoning.

She’s pretty consistent with it and uses the drawl almost every time she speaks a short a. I’ve never heard of such a thing happening spontaneously. Has anyone else heard of something like this?