My maiden queen has just had her first litter and she showed us when she was ready. Signs are panting, bracing of the back legs and moving around a lot to find a "nesting" area. Of course all cats are different, but just keep an eye on her and I'm sure everything will be great!
It would be ideal for you and your cat if you could find her a specific area to have the kittens, she might favour under your bed or other places where you can't reach her, so maybe sectioning an area off putting a tray and bed down for her and placing her in that area of an evening so she gets used to it.
As Ren said, chat to your vet and they will give good advice.