When cats are nervous, they don't play.

She probably can smell your previous cat, and she is worried
this cat will appear suddenly and the play will attract her.

Cats that have been living on the street, have to learn about
homes, and develop new interests.

Weezie has specific only things she likes to play with.
She loves the twist ties, which I roll into a spiral any sharp ends folded in onto the main part --especially black ones. She will play with me for a long time with these...I throw them on a count of 3...
and she chases them squealing with delight and brings them back to me. When my son helped us install the new flat screen TV he left these back ties on floor which she found and brought them to me! She likes my emory board I keep by the computer. She is always stealing it. Also the plastic sticks that come with plants from the nursery. When she was a kitten she loved the tinkle balls, but now less so. She chooses odd things to play with...for sure! I've always wondered if she has low vision, and only likes certain things for that reason? But she does catch mice and chipmunks and birds..so she can see outside well?

When we adopted Houdini...he had never been in a house. He was afraid of tinkle balls, or boxes, or bags, etc. But slowly he has become a toy connoisseur. His favorite are plastic springs, which roll around "seemingly on their own" . I found them at
Amazon: very inexpensive too!
http://www.amazon.com/Ethical-Wide-C...9724260&sr=8-4
He loves these, and Weezie won't touch them. Now I have toys all over the house. Houdini carries them around and dumps them everywhere! Houdini was afraid of tinkle bells for a LONG time and still is leary of bell sounds.

I think you can try some quality cat nip for her. This tends to make for a playful mood. Also we find play time often comes after eating. That is when our cats run around alot.

One game they all love is "mouse under the covers". You play this by putting a cloth or towel down on the couch or floor,
and move a stick or toy mouse on a string under it. You can use your hand, but be careful if the cat is rough you will get bitten thru the towel. Do this gently making a little scritching sound --this is why I use a stick or like my bamboo backscratcher.

Basically there are 3 types of games. Birdie, mousie, and rabbit. Birdie is string on a stick or a feather on a stick etc, that moves thru the air. Mousie is under something like I described and mimics a hiding mouse, and rabbit is a chase game two cats play and wrestle and tag each other.

One store bought thing both Weezie and Houdini play with endlessly is the donut plastic circle with a ping pong ball inside that they try to catch. We've had this toy for over a decade!

This is a variant on the donut type, that I am considering for us now:
http://www.amazon.com/Hagen-Design-S...9724260&sr=8-5

I think your kitty is going to need some time to learn the other
cat is no longer there. When she feels safe, and understands the other cat will not zoom out of hiding and jump her, she will begin to play. Use a very soft encouraging tone of voice too..some cats are really afraid of loud things or loud voices.
I can whisper a call from another room and both Houdini and Weezie will come! (BTW Houdini is playing with his spring as I type this! )

All cats love boxes, so try leaving a couple around, different sizes, and see if she goes in them, to hide or be safe.

Gently invite her with the string. Start slowly, and don't move quickly or tensely, slowly tease her interest with it, and use a encouraging soft tone. Cats study the "toy prey" and move slowly to catch it. So be patient and tease her and do things slowly...and she will get interested. Fast movements may startle her. This is the opposite of dogs IMO.
In our house I have words for the toys...the string is "stringywingy" The cats love funny words and it adds to the game!

This photo is of Oreo, playing with an old string on the dock upNorth. Simple, and one of her favorite games. She loves any string thing.