Feral Cat and adapting to inside

Hi Everyone! I'll make a long story short. I'd like to bring Miss Penny, a spayed feral into my apartment. She eats inside each am and pm, rubs her body on the doorway, purrs, and responds to my voice. Unfortuneately she has introduced fleas into my apt which I am managing, but the situation is not resolved. My indoor cat, Cleo, now has fleas. I flea comb 2x day and vacuum/ clean each day. There are no fleas jumping and biting anywhere, I've never gotten a bite and, except for the flea combing do not see any.
I'd like to trap Miss Penny, have her vetted and set her up in the room that opens to my balcony where she currently hangs put. But I'm concerned that if she picks up even one little leftover flea in the apt, then, as I can't handle her...not possible to flea comb.. I'll have an outbreak. This morning I gave her Capstar and I'd like to know if there is a safe follow up crushable flea preventative I can put her on. I'm also considering doing the same for my indoor cat but nervous. She has never been on flea control because I've never had fleas in the house. Any suggestions? Thanks!

I would get to the vet and ask for some Revolution for both cats.  I would then continue to use it for a few months.  This will stop any fleas for getting onto your cats. 

Be sure to get the new kitty to the vet before doing any introductions between the 2 cats.  You want to be sure she has a clean bill of health first as well as vaccines too. 

You can try to start feeding her in a carrier and see if that would be a way to quickly get her to the vet.  Yet a trap would definitely work too. 

Okay, yes, I'll try the revolution. This is all nerve racking! And she's so adorable. Very feral, frightened, but not aggressive. I'd love to get her inside before the cold arrives. I hate the idea of using chemicals on the cats, but it seems that is the only option. Thanks!