Well, as somebody who is often puzzled and perplexed by the behaviour of my computer, when I have a problem and I try various things to fix this (without really knowing what I'm doing) and then suddenly the computer starts working again, I'm just so happy that the computer is back to normal, I don't really care how the problem was solved. At this moment I might well say: "If it works, it works!" (and who cares why or how...)

The point is that you fixed the problem without diagnosing what the source of the original problem was. “If it works, it works.” expresses a satisfaction with your performance, even though it might be considered as a less thorough repair than completely figuring out what went wrong and taking steps to preventing it from recurring.

It’s an expression of resignation. Something is broken, someone goes to fix it, but the owner has no expectations of the repair working. The owner has given up hope that the broken item can be fixed, so, “if it works, it works” [but I don’t have much hope that it will work]. The owner is resigned to the fact that the item will still be broken.

Hello, Insik ~ it’s possible she meant one of two things: 1) If the program was faulty, but still useable, she might have said “If it works, it works” due to her indifference of the program to be at its full potential or not. In other words, she didn’t care enough to be bothered by its malfunction. Or... 2) After you installed it, you might have done a subpar job at that, but was still useable enough to be used until better installed. Cheers.