Well, perhaps it's just me, but the name "Mitsiko" doesn't sound too Japanese to me because of the "tsi" sound, which doesn't occur in standard Japanese, as far as I know. Are you sure her name wasn't "Mitsuko"?
Oh, by the way, JWPce, my Japanese word processing program of choice, has a rather large database of names, and "Mitsiko" isn't in it.
Oh, "Michiko" 'works', by the way.