I'd vote for one of the less expensive Shimano SPD pedals; the main reasons being that it's never a bad idea to have a double-sided pedal, and about two hundred different shoes are made to fit the cleats. Have your wife try on every possible shoe first--find the shoes that fit her the best and let them tell her what pedals she will have. One note--if she has very small feet (Euro 38 or smaller) Look road cleats don't work well on really small shoes.