just don't get in their face saying, "smile!" when they don't feel like it.
be there for them.<br />
find out what they like, and do it for them.
I suspect it would be the same way you would eat an elephan: one bite at a time. First step would be to get a professional in the picture to do a proper assessment. Second step would be to let the person know tha tyou are there for them. That smile may take a long time with a lot of work, but if you find the right combination of help and timing, ther emay be potential there... Good luck.
Bring a bunch of things they like to do with you or one of their other friends<br />
Or just let them vent then make a joke about yourself or tell embracing stories about yourself to keep their minds off the heartless
If you caused her to feel that way, then I guess try getting hit by a bus in front of her???? Jokes.