when you say it is her very back molar could you be more specific. is it the first, second or third molar. if it is the first molar then definitely yes, assuming she has a lower first molar in occlusion. if it is a second molar it may not be necessary since the lower second molar would be in occlusion with the upper first molar and would not hyper-erupt. it would be unusual to place an implant to replace a third molar. most of your chewing is done on the 2nd premolars and first molars. as far as esthetics is concerned you would have to see how much shows when you smile. most of the time you can only see the first molar. if you decide to have an implant it probably would be best to have a bone graft done at the time of the extraction.