I would really recommend that you take her to a nice place MORE than one night. You did leave that as an option when you said "at least one night". If money is an issue, maybe only buy drinks and desert for one of these meals.
My list?
Absolutely, Casa Picasso. It's the best food and atmosphere, although the atmosphere is not the most fancy.
Also pick at least two of the three:
Capricorn, Rendezvous or Rojo Lounge
I guarantee, these will all be meals to remember.