Maroukla is definitely not Russian, nor is the other sister's name,
Helen. My guess is the author translated/misunderstood the original name.
However, I have read the fairy tale, and as far as I remember, the good sister's name was Marfushka. Marfushka is a diminutive form of
Marfa. Maybe Maroukla is a very twisted version of Marfushka.
Finally, a Google search reveals a whole bunch of Greek Maroukla's, but resident Greek
Pavlos (who's been
MIA) might know whether that's a legitimate Greek name.