So one of the important things to remember is a cat does not require social contact with other cats to be happy and healthy.
Another is the time it takes to get them accustomed to one another: it involves keeping the new cat in a seperate room, and allowing them to smell each other through the door without seeing each other. Gradually you increase contact, every 1-2 weeks, and then swap the new cat into another room, so current cat can smell the original properly. Feliway Friends can help with this, as it's a synthetic Appeasement pheromone (the one cats release when they headbutt their siblings and mother). Feliway Friends is best used before adopting the new cat and during the entire time they are getting accustomed.
It's important to remember that your current cat may not ever warm up to the new cat. As she has been a single cat household this whole time, she may not ever be comfortable. Not saying it can't happen, I had four cats at once (many years ago) and while they weren't 'friends', they didn't fight or anything.
Your current cat may just see you as her family, and therefore would not take kindly to another cat encroaching on her 'territory'. You would also need seperate food and water bowls, and litter trays, for each so as to limit resource guarding and aggression.
I've wanted a second cat, but I also know my current cat just isn't into other cats. He loves people, but really doesn't care for other cats. So for me, it isn't a good idea to stress him out by introducing another cat into his territory.
As I said, don't take this as a 'dont ever get a second cat!" But more as a 'these are things to consider before doing so'. :)
Apologies for the text wall, and there are always exceptions! There are cats who love being around other cats, so it's hard to know truly how your puss would react! I'm just really passionate about cats and cat behaviour and science, so just imparting what I know :)
Edit: I will add, that generally female cats form bonds with other female cats easier, than males! Males are generally kicked out of the bevy when they reach sexual maturity (herd of cats), and if resources are plentiful the females will stick together. So it may work out for your cat if you adopt a female kitten (spayed ofc! Spayed cats are healthier in general!!!)