Don't worry about them mating. Without a nestbox they probably won't even consider it. It takes most people a lot of effort to get parrots to breed, lol. It's way more complicated than chickens or dogs. If you do decide to adopt her, introduce them slowly. They get jealous very easy and my fight over cages. Definitely don't put them in the same cage at first. Otherwise it sounds like a great idea to adopt! Even if there was a one in a million chance that they did mate just take the eggs away the same way you would a chicken.
ETA: Yes conures CAN mate with different species of conures but it's even harder to get 2 different species to mate, haha.