She can lay eggs and leave them cold. After about ten days, fertility will start to degrade. You should still have fairly good hatch rates with (properly stored) eggs of up to eighteen days old. Eggs should be stored air-cell up, in a cool, moderately humid place. If you want to tempt her into being broody, I recommend golf balls. She can't tell the difference, and you'll be able to store the eggs under best conditions. You'll also be able to label them with dates, so you can set your freshest eggs under her when she does begin setting.
If she starts setting before fertility degrades beyond salvation, she'll need to keep the eggs warm for nine hours to jump-start embryo development (that's how long a chicken embryo needs, anyway.) After that, she should not leave them for more than an hour or two at a time, because they've started to grow. After an embryo starts to grow, there's no turning back. Either it's kept in ideal conditions and it develops, or it dies.