i would get a colllar if i were you. a few quid for a collar and a few days of annoyance for her will be worth it to save the hassle and expense of her taking her own stitches out!
alternatively, put a baby vest or t shirt on her, put her front legs through the arm holes so she "wears" it. this is usually better tolerated than a "cone" and if done right it will stop her getting at the stitches. you just need a bit of creative hole making so her tail can go through it and she can go to the toilet.
When mine was spayed, they put a cone on her. They don't always though, only if the cat is in danger of pulling out the stitches, unless she's paying special attention to it, I wouldn't worry.
I swear mine got depressed because of her cone. It was so scary, she wouldn't leave the sofa! Very blue little thing she was. She did have some bruising from the op, I could see it under her skin and took her in 'cos I was worried it was bleeding. They gave her pain killers.