You'll have no problem getting a taxi to that part of the city within 15 minutes. I tend to use Taxi Taxi when calling for cabs in/around santa monica. If it happens to be raining -- then could be longer, but you never know when that 5th day of rain this year may come.

She could also grab a couple drivers business cards at the hotel and try them directly when she is ready to go.

The part of town where the relative lives is not likely to have cabs roaming the streets, so a call would be necessary. There might however be cabs standing by around the brentwood mart -- where there are a few restaurants.