C.C.
You may want to do a search of the mamasource site because this is a topic that comes up frequently and I know I've responded to it many times, especially since two of my three children sucked there thumbs. From my experience 16 months is too young to try stopping it. The rule of thumb (unintentional pun!) is that if you get them to stop before the permanent teeth start coming in (about 5 years) then it shouldn't have a negative impact on her teeth.