This must have been taken in the Jane Fonda-Oliva Newton John "Lets Get Physical" time frame  or soon after-there's no doubt in my mind it's Chissie.
By the hair I'd guess 1983-that's the year she was wearing her hair long and straight with that twisted hair band-very sexy to a young kid like me.
The other give away is her thin frame. In 1981 she was so thin at one point there were rumours of anorexia going about. She added a little weight back but was still thin in 1982-83. I'd be willing to not only bet that's Chris-I'd say you can safely date it to 1981-83.
BTW-have you seen the Evert photo later in her career when she is on top of a motorcycle-I have a signed photo and treasure it!