Stray cats keep coming around

About 2 years ago, we had a stray cat that started hanging around our house.  Long story short, my husband started feeding her, and now she's ours.  After we gained her trust, we started inviting her inside.  However, the cat we adopted from the Humane Society as a kitten is a bit of a jerk (that's a polite word for what we affectionately call her), so they've never figured out how to cohabitate.  As a result, Kitty #2 lives outside.  Unfortunately, other stray cats have started hanging around in recent months.  They eat all her food and leave her acting skittish and nervous all the time.  I can't afford to start feeding them all (because then they become our responsibility, and the vet bills would eat me alive...4 animals is more than enough!), and even if I could, they make our sweet angel kitty nervous.  I hate that she can't relax at home.  I called the animal shelter, and they were no help.  They will allow me to rent some traps for the cats, but I'm guessing our kitty would wind up in them more than the strays, which would exponentially increase her stress.  Do you guys have any suggestions that may help me get rid of the strays?

While you're leaving food outside, you will never stop the strays from coming around.

Would it be possible for you to very gradually re-introduce your outside cat to your inside cat?  There is a lot of good info on this site to help.. I know they have already met, but if you do it 'by the book' you could just make it work.  Have a look at http://www.thecatsite.com/a/introducing-cats-to-cats

I really hope there is some way you can make this work.. I feel sorry for your poor outside girl..