Definitely try to convince your daughter to live at least 1 winter in NH before selling the condo. Although my DD always wanted to live in Paris, just 1 winter did her in. She misses the sunshine, the warmth & more importantly her family. She hates being so cold, the constant rain, short days & the overall dreariness of winter there. She plans on moving back to the sunshine of CA before next winter.
In the meantime as far as transportation goes, I've always been impressed with the many low-cost options here for seniors so I googled it for San Diego. Here's an article I found
https://www.sandiegouniontribune.com/caregiver/caregiving-essentials/meals-transportation/sd-me-caregiver-seniors-mobility-20180424-story.html Its from 2018 but lists many services available - some of which may still be operating.
Just don't rush into anything just yet. Good to look into your options, but unless you are excited about something you find, just stay put & make whatever adjustments you need to until (or if) your daughter makes the move permanent.
Love you!