Katie's right. Before you give up, give it another try. We know nothing about how you introduced them to begin with - but cat introductions have to be done on their schedule, not on our schedule.
Your newly adopted kitty should be kept in a separate room - a guest room, someone's bedroom - a room that isn't so important to your Lucky. Put a litterbox on one side of the room - put food and water on the other. Make sure kitty has places to hide (boxes are great for this), and toys to play with.
Cats are very territorial, and "making introductions" is about getting them comfortable enough with each other so that they can either share the territory without fighting, or so they they both agree on which one of them is the boss without too much fighting for the position.
It is natural for cats to hiss, bat at, and swat at each other - especially when they're first meeting.
The idea of separating them for as long as they need (can be several months!) is so they can get used to each other's smell and each other's presence. If you can temporarily replace the door to the room with a screen door, that is ideal - then the kitties can see each other and easily smell each other, but they can't swipe at each other.
If you can't put a screen door on the room, they'll just have to smell each other under the door. After a week or two, when Lucky is curious and near the door, open it just a crack so they can see (and smell) each other but can't get in or out of the room. Watch the interaction. If there's an immediate hiss or growling with ears back - close the door and give it some more time.
While kitty is separated, there are some things you can do to help the reintroductions go more smoothly:
Take several clean rags or wash cloths, and wipe "kitty" all over with one of them. Put the cloth with kitty's smell all over it underneath the food dish of Lucky. Do the same with Lucky - rub her all over with a cloth, and put that under kitty's food dish. Take another cloth, and rub it all over kitty. Put treats out for Lucky on that cloth. Again - do the same thing with Lucky. Take another cloth and rub it all over Lucky. Put treats out for kitty on the cloth that smells like Lucky. Do this every day, and remember to "freshen up" the smell of each cloth by rubbing it on the proper kitty each day. This helps the cats come to associate good things with the smell of the other cat.
When they're comfortable enough to just smell or look at each other (through the screen or through the very slightly opened door), you can begin to have supervised interactions. Bring Lucky into the room (don't let kitty out). Maybe try playing with a wand toy, or give each of them a catnip toy.
If there's growling or hissing, this is OK. But if the ears go back, or the hairs on their back stand up or their tails bush out - take Lucky out of the room. If you miss the signs and they actually start to fight, do NOT physically separate them - you could get hurt. Make a LOUD noise - shake a can with coins in it, or clap very loudly - this will startle them. Then take Lucky out of the room.
But with slow, gradual introductions, supervised, for short periods of time - you should be able to lengthen the amount of time they spend together without hissing, growling or swatting. They may need to do some of this to establish which cat is alpha cat - this is normal. We have six cats, and at any given time one of them usually has a scratch somewhere. :; But out and out fighting is not OK.
Just remember - the most important ingredient to successful introduction is time. And remember to spend lots of time with Lucky, reassuring her that she's still your special girl. But as long as kitty is separated, you'll have to spend lots of time with him too so he isn't lonely, and also becomes comfortable with you (or other family members)!
Good luck - and if you have any other questions, please feel free to ask.