Well, a female friend is still podruga, not padruga, and 'your' here would be tvoy (masc.sg.), not tvoi (pl.); the language did not change that quick in the part of its orthography. As for the complementary close, it has a double meaning and semantically is actually closer in the modern Russian to 'be crazy', but that mostly works in phrases like Они с приветом / Он с приветом.
This complementary close stands for any other one of the same structure, like
С уважением
С уважением к Вам
С наилучшими пожеланиями
С поздравлениями
С восхищением (if you want to flatter a bit when writing a romantic letter)
С пожеланиями успехов / удачи / всего наилучшего (any Genitive attribute would do).
The priviet also can be used, but then it would be better specified as a form of greeting, e.g.
С дружеским приветом
С английским приветом
С американским приветом
However, such a complementary close would be regarded by most native speakers as a manifestation of utter / absolute trust, which would really be a little bit strange for them.
The calques from English also would do, e.g.
Всего хорошего
Искренне Ваш / Искренне Ваша
С наилучшими пожеланиями