If she isn't running it really hard I'd lean out the oil in the mix a bit. When my kids were racing 50cc we could run 100:1 Amsoil at 100:1 till they got really good on 65 and 80cc bikes, then we moved to more oil, 64:1 with that 100:1 Amsoil worked pretty well. We now race our 125-380cc 2t bikes at 44:1 on cheapo walmart premix and they are just as happy. That is high RPMs, A and B racers.
With low RPMs and lugging around they can load up on oil, and not burn it as much as spooge it out. When it revs a bit it gets all that oil from the crank up top, there is your smoke (probably).
Don't be afraid to thin regular oils to 50 or even 60 or more :1 if she is basically lower RMPs with low loads. It'll eventually foul the plug if the engine isn't getting hot and fast enough to burn or expel the oil.
Keep an eye on the gear oil level too, in case it has a bad crank seal but then it would be over rich on oil all the time.
Of course, you can join in the nutty premix oil thread too!