Introducing did not go well

My barn cat, Slick, was brought in in March and had 6 kittens. She is seperated by a screen door from my 7 other cats (mostly all seniors). She was feral, but she tamed down real quick, within a day or two I was rubbing her belly. She did not revert to her feral state after the kittens were born. I am left with her and two kittens who are now 6 months old. The kittens get along real good with my other cats. They go back and forth between the workshop they live in with their mom and the other two rooms where my 7 are. Well, it is going to get cold here in upstate New York soon. The workshop is not heated, but gets heat from the rest of the house through the screen. Anyway....yesterday I decided to see if Slick would get along with the rest of the gang. After all, she has been nose to nose for 6 months through a screen. Her body language during that time was good, even laying down and playing beneath the door with the other cats. Well, it did not go well. She immediately got a bead on my female cat Gel and it was not violent, but it could have been if we hadn't been standing by with a water bottle and broom. I realize that Gel is the alpha cat and so is Slick. I did anticipate a problem. So now Slick is back in the shop. She does have it good because she has access to the outdoors and a lovely run my husband built. But it is a hassle and would be so much easier with them all in one area. Any suggestions? Thanks in advance. Poor Slick.

Yes, Slick is spayed (they all are and tested). I guess I know it's going to take time, but it is so stressful. Yesterday after the attempt, they were all looking at each other like "ok, you want to start something?" Tails were fat. I have such a nice little eco system here. Everyone getting along good. I don't want to start world war 3! My husband thought she felt threatened because they all entered her space (the shop). I see your point of her not being totally feral. She was always the least skittish of the barn cats. We will try again, don't want to get in the middle of something either. Been there done that, (not with any of my current brood though). Will let you know if mission is accomplished!

I do play with Slick. I even bring her and her kittens in and put the others out in her place so she can have a change of scenery. She loves to run around in their room. It seems to energize her. I agree with you about her bullying. Little snot We will keep trying. The heat will have to go on at some point and I will not be able to leave that door open to the shop. However if it takes longer to acclimate her in with the others, I can bring her in and close another screen door between the heated rooms. Just a real hassle and would definately prefer not to have to go that route. Thanks for the info.