2009 Buick La Crosse car won't start

My mother who does not drive car often 1-2 times weekly has been experiencing a dead car quite often. The dealer is telling her there is nothing wrong with the car. They say she has too many accessories on the car and that she just needs to start is every day or every other day. What crap. She couldn't find one without
My personal thought is they could have at least offered her a new battery. This has been happening more and more and usually someone will jump the car for her and she is happy. She starts it one day and it will not start the next day. She is 85 years old and is losing her mind over this (not to mention sleep). She will not stand up for herself to the dealer and does not want to let me take control. So far this has only happened in her garage but I don't want her to be out somewhere when this happens. Can you shed some light on problem