i can tell by the thickness for a start and when filling there is a certain 'fishy' smell to it. soaking off the MMA takes longer, and its rubbery consistance.
New clients should always have a consultation before treatments, this helps you to give her the best advice and nail enhancements to suit her life style.
if you are still not sure whether its MMA, ask her where she had them done, and always soak off and apply a new set of enhancements.