Maria is the second most used feminine name in the world. It is very popular but international and used throughout the centuries, so won't become dated or associated with one time period.
Jennifer is a lovely surprise in the middle.
I also really like the option of MJ as a nickname if that would suit her personality.
I live in the UK where nicknames ending with "z" are common (Caroline becomes Caz, Jeremy becomes Jez) and I have met a Maria who goes by Maz.