Night time toilet training

Hi IM's
My little lady is 3, she was so easy to toilet train at 2.5, she basically done it herself. She has still been wearing nappies to bed, she can go up to a week with dry night nappies, so i thought she could use what we had left then start wearing nickers to bed. Well we ran out of nappies, first night no accidents, the next 2 she had accidents. She doesn't realize that she had done them and wakes up clueless but gets very upset.
What should i do, is she ready? I don't want to force her to do it if she is not ready, but i don't want to buy more nappies if shes going to need them. Like i said she was so easy to toilet train because she was ready and has had very little accidents. Is night time something that one day she will just be ready for? I really don't want to be washing sheets everyday :/
Advice would be appreciated, Thank you :)