Per the TOS though you can't share between husband and wife, only 1 adult and 1 child on the same account. Most of us don't like that policy but it's the rules. True you are probably not at a big risk (same ip, same computer, etc.) but why risk it at all? You could help your GF level her own toon(s) easily.

Edit: and with premades on the PTR she could try out 4 different classes!