This is a hard one.
Now, if she relocated to SF, she could easily get to the city and live around / near it
SF has a more urban feel definitely, more bums, more crime, but also more culture and definitely its a lot more poppin in SF
Mountain view and that area has alot more 'hispanic' feel to it, just because the surrounding cities and areas, San Mateo, Redwood City, etc. have sizable hispanic populations.
Id say if youre lookin for a more 'nightlife' type experience go SF, if youre lookin more to chill Mountain View is the area
Its weird cause every city / area has its own feel
If she moves to SF, you can live in Pacifica / daly city/ south city, or san bruno
If you need sunshine and warm days, stay away from the SF/Peninsula area
Peninsula cities:
Pacifica - more white folks, asshole cops, nice scenery, lot of fog
Daly City - alot of asian people, not much happening, giant bedroom community, foggy as fuck, moreso than Pacifica
South City - diverse, also somewhat of a bedroom community, gets cold and windy often
San Bruno - you can either live in the 'lower income' area or the 'bedroom community' area, lower income area (east of the tracks/aves) has best weather