The person you describe is best taken care of by keeping things simple. I would put a couple of gallons of water in her trunk. I would use store bought drinking water in 12-16 oz bottles. Find some that have a fairly long shelf live and can be frozen with out breaking. I would do the same thing with food keep it easy to fix, cheap to buy with long shelf life & bought at the local store. Put a warm sleeping bag in the trunk along with wool blanket, coat, hat, gloves and a good pair of boots. Store all of this in her trunk in a duffle bag. Securing the bag across the space behind the back seat keeps it out of the way. Put a decent first aid kit and a good LED flashlight and spare batteries some place handy.

Change out water, food and batteries once a year and use your $3-5k somewhere else. This is not a thing to throw lots of money at it is something to put a lot of reasonable thought in to as to what will serve her at her experience level best.

The person you describe will best be served by sheltering in place whether that is at home, work or in the car. It would not only be more dangerous for her to sling all that on her back and try to hike some where but would seem very silly to me if she has no knowledge or experience with anything but a 4 star or home experience.

If she is open to it you might want to explore the safest parking (some place that will not get tagged or fall during a quake) for her at work and at home, you might walk through evacuation plans for the buildings she is normally in.

You and your mom will best be served by keeping it very simple