Keep them separate for as long as you have to. A resident cat will almost always take exception to a new cat no matter the age. And even though people always seem to think that a kitten will make the introduction easy (vs. an adult to an adult) but MANY adults do NOT like kittens. They are too bold and pesty. As your kitten matures, she will have more in common with your older cat and they should tolerate each other much better.

Keep swapping smells and only let them meet under supervised wisits and always pamper your old cat. Let her know she comes first.

Good luck.