In Russia, most Names have a standard pet form (eg. Girls:
Lena for
Elena,
Tanya for
Tatyana,
Masha for
Maria,
Sveta for
Svetlana,
Ena for
Irena; Boys:
Sasha for
Alexandr, Volodia for
Vladimir,
Vanya for
Ivan,
Kolya for
Nikolai, Seryoja for
Sergei etc etc).
Natasha is the standard pet form for
Natalia, but I guess your friend/ her parents can choose whatever pet name she/they want to for her given name, particularly when not in Russia.