Hi TP, sorry I haven't been around much. I certainly know what you are going through. We once adopted ten year old brothers who had been badly mistreated and clung to each other for support. When one died the other was totally bereft and would call for his brother all the time, it was heartbreaking. His medical conditions meant we couldn't give him a companion and it took him months to settle down.
When we can we help foster cats for our local cats sanctuary and when I get a new cat/kitten to look after I usually take the slow approach. The Kitten will be fine but your older cat will be the one that you have to protect. She has lost her sister and still has issues with that to deal with. Her natural territorial nature will be the main thing to overcome.
I try to keep the new cat confined to one room initially and I use Feliway diffusers in the rooms where both cats will spend the most time this chills them out and can make the whole process a lot easier. Swapping an article of your clothing, I use a couple of old tee-shirts, between the cats lets them smell each other - with a hint of you - to let them experience the other cat without any physical confrontation.
Putting the kitten in a separate room and letting the other cat have supervised visits normally gives an idea of whether your cat is willing to tolerate a new companion. It can take a week before the older cat shows anything other than disdain or pure hate for the new arrival.
Even when they both have free access to all areas don't expect them to always get along immediately, don't feed them next to each other and make sure they have separate litter boxes well away from each other.
The kitten will probably want to be closer to your older cat far more than she will tolerate and as has been said your cat will box the kittens ears if it over steps the mark, natural behaviour for a female cat, but you don't want the situation where you cat shows the kitten actual aggression as once this happens it is very difficult to overcome the fallout. So, if at all possible, let the introduction be at the resident cats pace, don't force anything, don't sit cuddling the kitten in her eyesight as you will be viewed to have sided with the enemy,
and trust her to guide you. She has had a companion cat previously so you are half way there.
On the other hand it could be love at first sight and she will instantly want to mother the new arrival.
Over the years we have had many resident cats and had to introduce them to feline guests and I don't remember a single one of them acting as I expected so good luck and I am sure it will work out.