Replacing infertile eggs in the Incubator

Ah lukeasmum, never mind, do you not know anyone with a few fertile eggs?
Although i would give her a few days/weeks if you do decide to put some under her, i might be wrong in saying that, but sure grannie or joyfull will advise if i am wrong, as they have a lot of experience in hatching under broodies, this is my first year.

Lukasmum, if she has already been sitting for 3 weeks I'b be reluctant to let her sit for another 3 as she may get debilitated though lack of food and exercise.

It would probably be best to de-broody her by putting her in a crate with no nesting material for a few days to break the broodiness.

Sorry your eggs were infertile

do you know anybody with a couple of very young chicks - day olds or a couple of days old? she may take to those. Dizzy Lizzie did this very successfully.
To break a broody I put mine in a cage for 2 days and 1 night - this breaks them every time for me - not 2 weeks 
I also agree with Casey if she has been broody for 3 weeks then let her recover before seeing if she goes broody other wise she will be on reduced nourishment for 6 weeks which could be seriously bad for her health.

I don't know  of anyone with very young chicks so unless someone here knows of a fresh
hatching in Bedfordshire, I think I will have to cage them for 2 days as Joyfull suggests.
lol all that expectation!

Fantastic idea.  Well done you.