For a second I thought this was going to be another girlfriend for Ferrari swap
(had to Richard
)
You're in SF...pack a gourmet lunch and drive her up the coast for a nice picnic, then give here a nice sparkling piece of jewelery between glasses of wine (not a gift that'll get you hithced). Going big and flashy has less impact then something the you apparently spent time planning...my current and formers seem to always melt over activities that appeared to have been well though out ... key word "appeared" to be.
Have fun.