Ohh thank you so very very much, all these are things I didn't know! -
The tray is removable so I shall remove it when outside as you have advised - I have a grit mix which is grit and oyster shell mixed, I will check the age limit on it and if not suitable I can get a different one for the baby.
There are a lot of people here who don't bother with integration, a popular method is to just put the new birds in with the flock at night time and then just let them out together the next day and just leave them to fight it out - I've said no to it, I want to give all the birds as well as us, time to adjust and to get used to each other, plus I want to keep the baby safe. - Although friendly this hen was part of a production line - so to speak - she has come from a flock who's purpose is to lay eggs for selling and for hatching - worker hens as I call them are not tamed - my friend is one of the biggest sellers/breeders in Suffolk where I live, his outlay is such that there is a very high probability that my RIR's came from a line which began from his eggs, even though I bought them from a dealer who breeds and hatches his own flocks - this hen will be used to the hustle and bustle and busy life of a production farm, so we have to work to tame the bird as well as integrate it, so I know it will be a long and slow process - as long as I have them sleeping together before the onset of winter, I will be happy. Also we want to win her trust enough that she will allow us to handle her chick, we want to get it as used to us as much as we can. I know my girls so well and I know they won't be a problem, I just don't know how the Sussex will be towards them, plus with her being older I think there is every chance she will challenge Pedro for head chicken status - mine are very much pampered pets and I think a hardcore farm bird is going to be a shock for them, so I intend to go very slowly and tread very lightly.
I can't thank you enough for all your help and advice and for sharing your wisdom and knowledge - I so wish you lived here, I'd have you tame and integrate them for me