If she is a rescue, she may never have learned to play. It will take time & patience. Some dogs have less play drive than others, however. So I (or we) have no idea - which boat you are in.
You indicate "when she does play" it just doesn't last very long...but you do not bother to tell us what has worked, and what has not. Do you praise her, laugh, sit ON THE FLOOR .....WITH HER?
A lot of MY dogs like soft squeaky toys. The problem is, they don't last long if I do not pick them up - as they get "gutted", so we have "play sessions". Kong still makes some soft toys like this.
With puppies, I usually try games of "KEEP AWAY" with a towel being dragged on the floor - via a piece or string. I can make it jump or wiggle, etc. (I don't know if she would like that or not, or like it better if this was a squeaky toy like a long skinny fox or worm.) The Audubon company made some life-size or larger stuffed toy BIRDS that make bird sounds (via a battery) - and for sporting dogs; these can be fun.
You might also want to try scent games or nose work - where you hide some treats & encourage her to FIND them. The games (hiding places) can get harder, as she gets better at finding the treats.
Not all dogs have a strong retrieve drive. While it is great if they do, you may find she likes a suede or leather glove BETTER than a tennis ball - when tossed. (I do tracking, and we are ALWAYS finding uses for orphan gloves..... we don't go out and ruin a perfectly GOOD pair!)
Finally, playing WITH another dog - (who does know how to play) can help her. She will watch its interaction esp as it works for its owner and may see the dog having fun - and want to do something it sees.