Focus on the stuff she already knows how to use. Spare clothes, water, food. A sleeping bag. A good torch or two. A whistle. Toilet paper. Whatever medications she already uses.

I wouldn't bother with the water filter or other treatment. No trapping devices. No bivy - she can sleep in the car as long as she has the bag to keep her warm.

I'd give some thought to money and/or trade goods, but I wouldn't want her to become a target for thieves. However, she may do best in collaboration with other people so give some thought to how that would work.

Does she know how to use the car radio? Does she have a mobile phone? Can she send text messages? (Text is often more reliable than voice in a crisis; it demands less from the network. Make sure she knows that.)

A lot depends on her. Older people are often more robust than they get credit for. She's survived this long OK; she has a job, she's raised children.