There is no advantage for you or her in adding her to the lease. It just gives the landlord an advantage because there are more people to go after if the rent is not paid. Most leases say that everyone named in the lease is "jointly and separately" liable for payment. In other words, each person is 100% liable for 100% of the contract rent. Even if you pay your half and the GF stops paying, the landlord can come after you for the missing rent.

Check the lease you signed regarding house guests. My lease stipulates that guests that will remain longer than two weeks must be reported to me. I have one tenant who said this would not work for her due to some special circumstances, and her credit and reputation are strong, so I removed it from the lease.

4Driver4

"Never give up the throttle until the bitter end." -RC

1990 Coupe Q
1999 A6 Sedan Q 2.8
2000 A4 Avant Q 2.8
1995 Mazda Miata: the anti-Audi
1999 Chevy Suburban: the anti-earth :-(
1990 Nissan Pickup: Snow plow/garbage hauler