Her personality was intended to be modeled after Sarah Connor from the Terminator franchise, even saying, 'Come with me if you want to live,' when she rescued Woody and Buzz from Sid's mansion, with Woody remarking in reply that he 'wished Woody was anatomically correct.' After Toy Story was a success, Mattel decided to put that policy aside and allowed her to appear in Toy Story 2, and also with her boyfriend Ken in Toy Story 3. It was common knowledge that Disney had been unhappy with the original scripts of Toy Story for some time and Mattel was concerned about the effect it would have on sales.
Also, they didn't want to partake in a film with a troubled production. However, Mattel would not allow the use of Barbie because they didn't want her to be given her personality (it was important to them that the girls who buy the toys would imagine what Barbie is like themselves, thus making the toy unique to each girl). Barbie was meant to appear in the original Toy Story as Woody's girlfriend, in place of Bo Peep.
