I would try to encourage her to bond with your other cats also. Pet them together, play with them together, so the little one will begin to see one as a friend and replacement mom.
Also, can you confine the cats to a kitten-proofed room while you are at work? Maybe with friend some days? When Squirrel had her litter I ended up confining all of them to my bedroom that had been kitten proofed and had a litter box, food, water and tons of toys. I started this about 8 weeks of age and continued until they were about 14 weeks old. They all were very glad to be released when I got home but overall I think they enjoyed having the big room to play in. This would also help the kitten learn to socialize with your existing cats.
Good luck, and don't worry, soon she will adjust and they all will be best buddies.