If her laziness is not depression then it can be
that she has no personal motivation (desire)
she lacks ambition.
Physically she can be drained from laziness
I know that the more I sit around the lazier I get and the harder it is to get up and get busy. The more I do the more it energizes me and I feel like I could work non stop. Laziness actually does physically and mentally drain you!
Why Exercise Makes You Feel Great explains how exercise makes you feel more motivated
when I sit at home with nothing to do I always put off things like I still have this afternoon to do the laundry and I don't have anything else to do. Then by the afternoon it is I'll do it tomorrow.
In December when I am laid off I don't do anything because I feel like I have an entire month to get it done. When I am working I am always fitting everything in to get it all done and it is more like a challenge.
Have you tried making a chores list, telling her that is what you want done by the end of the day?
Maybe cut her off spend money?
Maybe tell her that if she doesn't start doing anything around the house then she must go out and get a job but you are not having her sit around like a free loader.