There's nice areas in Culver City and the neighboring Palms and Mar Vista areas that will at least sort of split the commute. UCLA is much closer to these areas, but if parking for law students at UCLA is anything like it was when I was in undergrad, your girlfriend basically will not be driving to school. (Parking permits are nearly impossible to get unless you are a TA and/or live at least 25 miles away, and you'd be shelling out close to $2k for the year just for permits.) There's great bus lines in all of these areas (Culver City Green and Santa Monica Big Blue), and when I graduated in '07 students could swipe their BruinCard and ride for 25 cents. You can get to USC in 20-30 mins most of the time, and probably similar on the bus to UCLA.
From what I understand, it will be way easier to get a parking permit for USC, plus living on the Westside is probably more fun, and commuting from the Westside to USC is easier, traffic-wise, than living in Echo Park or Silver Lake and commuting to UCLA. Nearer to UCLA, North Westwood Village itself is party-hardy and where all the undergrads live. South of Wilshire (still in Westwood, more or less immediately south of campus by about a mile), is within easy walking distance for your gf, is more populated with young professionals, grad and medical students. The complexes there are also more modern (read: underground parking), which is a huge asset in this area because street parking is a complete bitch. Similar housing stock is available in the greater Westwood area, closer to the 10 freeway off Westwood Blvd and Sepulveda Blvd. (mostly north of Pico), off Beverly Glen between Wilshire and Santa Monica, and on the blocks immediately south of the Wilshire Corridor between UCLA and Beverly Hills.
There's good housing options as well in the Santa Monica/Brentwood areas (but it will be more expensive), and basically all of "Los Angeles" proper between UCLA and Santa Monica.
Mid-Wilshire, Park La Brea (aka the Grove area), and WeHo have options as well, especially in terms of splitting the commute, but these areas can vary in quality pretty quickly so be sure to visit in person. Also, commuting to either school from here would blow. (It may look like two miles from UCLA on Google Maps, but unless you're used to LA traffic, that'll easily take you an hour in traffic, via car or Metro Bus.) Getting the 10 freeway from here or using any of the major East/West arteries to get to USC also gets bumper-to-bumper pretty damn fast.
Then again, traffic in LA sucks everywhere so just be prepared for that. And keep in mind that the LA Metro's Orange Line/Expo Line will be serving the USC area soon. It's a light-rail/above-ground subway that's been under construction for a few years, starting in downtown and stopping literally 20 feet outside the USC law school on Exposition Boulevard. It will continue westward, with service as far a Culver City/Palms/Robertson expected in 2011 or 2012 I believe. May not help you this year, but it's something to keep in mind for later years.