Speaking seriously, she's probably in depression, and staying isolated in her home will prolong it. She should try volunteering at her local library or a senior center, get out of her home and out of herself.
As for exercise, she needs to stop focusing on how she got where she is - learn from it, but not beat herself up with it - but use that as her starting point to expand those limits. If she can walk a half mile, she should go to a community center or high school oval track and walk two laps (~1/2 mile) several days a week for a week or two. Then up that to 3 laps per visit for another week or three. 4 laps is a mile or more. Once she's up to a mile or so she could gradually increase that by walking around her neighborhood or a nearby park. It's work, but it took decades for her to get where she is, and if she wants to change that significantly in just a few years, it'll be good hard work. There's no 4-week couch-to-half-marathon programs out there. And by using community center tracks, park trails, and her neighborhood streets, the cost will be a pair of shoes and an exercise outfit or two. And she might meet and make some friends at the track or on the park trail.
BTDT, got a couple dozen race T-shirts.