Be sure she carries a mobile phone. Then, if she can't get into a shop, she can call and ask the staff to assist with door opening.
Longer term, she may wish to let these shops know that she can't patronize them because they aren't accessible -- a word which has come to have a connotation of things like wheelchair ramps, automatic or manual powered doors, aisle wide enough for power scooters and chairs, etc.
The simplest, a plate-operated powered door, is a fairly inexpensive modification, as these things go, and many shops will be willing to install one in order to increase their accessibility for wheelchair or crutch users. In some locations, this is required by law, but be careful pushing for legal solutions; the cost can drive a small business to close its doors.
One method I've seen used in parking garages is to go in and out where the cars do. There's usually a pedestrian walkway that bypasses the gate bar, and in my experience it usually has wheelchair cuts as well. If she's had to park above ground level, almost all higher parking structures have elevators (required by law almost everywhere in the USA); she could take the elevator to ground level first.