I start to litter train mine at 3 weeks, they are 6 weeks now and fully trained. I started off putting them in the tray after they'd eaten, also to start with they will poo on the floor, so what I did was put it in the tray and put the kittens in to have a sniff, they automatically try to cover it.
Kitten litter depends what you want to use, I used chick corn for kittens, then wean them onto what my adults use which is Sophisticat.
I would give her her own tray, but depends on how many you have in the house already.
I would leave kitten biscuit down all the time, and give kitten meat 3 or 4 times a day. leave water down 24 / 7 too
I would'nt recommend letting the kitten near the new ones, I keep mine separate from my others for about 4 or 5 weeks.

 

thanks hunni
i better start getting her trained then he is 5 weeks and still havent trained him..
ive got two litter trays at the moment one for each cat.. so ill just buy a smaller one for him thanks x

 

No problem, glad to be of help