How lovely Em.
At ten weeks old, it's still possible to socialise kittens who've been living feral. It's better to get them as young as possible, but sounds like this little girl may have a good chance with you.
The absolute key is patience, and not rushing your fences. We learned this the hard way.
The separate room for your new kitten is really good to get both cats accustomed to the new situation. Make sure there are few places your new kitten can hide in the spare room - ideally, if you can clear the room so it's empty apart from a cat box for her to use as a bed and a safe place, a litter tray, food and water bowls, that's best
(I once believed we'd lost 2 semi feral kittens in an almost empty bedroom. Until I looked inside the (fitted) wardrobe sand saw two terrified pairs of eyes peering back at me from the rear. How on earth they got the door open I don't know, but they did. In fact it was Fireworks night a year ago, so it's still pretty fresh in my mind.
)
Scent swapping is also good - and making sure you divide your time equally between the two cats.
Better still, if you can squirrel your new cat into the house while your other cat is out, or otherwise distracted, you can pretend the cat in the spare room has mysteriously appeared, and you can both be excited about checking it out.
Be prepared for some hissing and spitting and angry words, and remember - with your new kitten, food is key to getting her used to you. Make sure she associates you and other family members with the appearance of food or tasty treats. When we got the girls I was recovering from a spell of hospitalisation, and had a few weeks at home, which we spent just sitting in a room with the girls, reading, watching TV on a tablet, listening to the radio, chatting to my OH. They hid loads initially, but you could see progress at the end of each week (although I confess we almost took them back when we had a crisis of confidence - thank God we didn't - a year later and they're beautiful young cats - still a bit flighty, but loving and tolerant of being touched).
Might be a good idea to get some Pet Remedy plug ins and put one upstairs and one down (assuming you have an "up and down" and don't live in a flat or a bungalow). It's also good to use the pet remedy spray on your hands and clothing - it has a calming effect on most cats (Feliway is another calming plug in and spray pheremone). We also found that Zylkene sprinkled into all of the cats' food helped to keep the peace. You can get Zylkene online or at Pets at Home and other decent pet stores. You would need to get the size suitable for cats (not dogs) - it's not a prescription medicine, but it can really help, and its safe to use daily.
This is a really useful link:
http://www.theluckyfew.org/site/feral_cats.htmland this:
http://www.wayofcats.com/blog/cat-typesYou need a stout heart, plenty of savlon (just in case your little girl has a tendency to use her paws as weaponry) and shedloads of patience, but it's possible to make things work. Give it time. Let the cats go at their own pace in terms of introductions. Dont rush them. Don't lose heart (and if you do - remember us - we're always here to help where we can).
One of our members, Liz of the Clan Cats, has a large number of ferals and semi ferals they've successfully adopted, and by and large they all rub along well. She will be able to offer advice too, as will Paula (Judecat) and Sheila of Waltham Forest Cats Protection.
I hope this may help too.
Sending lots of positive vibes your way and hoping this goes well for all of you.
If it does, we'd love to see piccies.
