Something to consider, most of the posters on this board think about going to the gym and lifting to "get in shape" or "loose weight". She may not be into the idea of a gym. She may think it's what she needs to do but her heart is not in it. Try finding an ACTIVITY that she is interested in or wants to try.
Maybe she likes/interested in (or played in her youth) tennis, basketball, swimming, soccer,riding a bike or walking around a park... whatever. See about getting her invovled in one of those activities. It could be getting her into a YMCA or city league or going with her to the community pool/park.
If she enjoys an activity, she's more likely to keep doing it. Especially those first few weeks when with all those aches and pains. The weight loss/health benefits will start coming once she gets moving. You can always branch out after she takes those first few steps.
As for the diet aspect, take a look at small changes that won't radically change her lifestyle but will have a big impact. Without a major commitment on her part major changes will be unlikely for her to stick with over a long period of time.
Some examples, if she drinks soda, can you get her to cut it out or switch to diet or back off from 64oz/day to 12oz/day? Does she have a bowl of ice cream each night...get her to go with 1 scoop instead of 3 or switch to lower calorie option like frozen yogurt or use fresh/ frozen berries instead of chocolate sauce. You get the idea.
Add up a few of the little things plus some physical activity and she will be dumping hundreds of calories/day.