They left a big concentrator for use around the house and 15 small bottles and 4 big bottles for emergencies. She feels better already.
If you use an "intermittent regulator" on the oxygen bottles rather than a "steady flow" regulator you will get a lot more time per bottle. Concentrators come in two sizes. The big ones are for users who require more than 5lpm. The smaller ones are the ones most users have and supply from 1 to 4 lpm. Also keep at least one bottle set up and ready to go in case of power outage. Regulators are not easy to attach and set up correctly without any available light. I purchased a couple of portable concentrators because using the bottles is just not my thing especially on a trip or even around town.