Hello, Janis and welcome!
Most new cat introductions are difficult, especially with a 'senior' cat like Daisy, who is set in her ways and used to being an 'only' cat (I'm assuming you didn't have any other pets until your daughter brought her 2 cats with her). The younger cats are more active and want to play, but Daisy sleeps most of the time, and probably finds them annoying and 'in her space,' which is why she hisses and growls when they get close. She also feels the need to protect her territory, since these two 'intruders' have suddenly appeared, to share her space.
It's important that Daisy has a 'safe' place to go to where she won't be bothered by the young ones. If you don't yet have one, a tall kitty condo or cat tree is great, because there is a platform up top for cats to sleep and to 'survey' their world. I think she'd feel safe up there. Also, try the scent transfer method, which is taking a very slightly dampened cloth or paper towel and pet Daisy, then pet one of the other cats, then pet Daisy again. Repeat this with the other cat, too, and do it as frequently as possible, every day. This will deposit each cats' scent on the others' fur, so Daisy can get used to them, if she smells them on herself all the time. You can also take an old t-shirt or other small article of clothing with your scent and pet all the cats with it. This will equalize the scents on them and your scent will help make Daisy feel safer and more secure.
Here are some great ideas for introducing new cats to each other:
Everything must be done gradually and not rushed. Also, when Daisy DOESN'T spit or growl when she's near them, reward her with a cat healthy treat and praise her verbally.
Make sure to give her lots of extra attention, so she knows these two new cats will not be taking you away from her and she's still your favorite, furry girl!
Get some Feliway plug in diffusers; these emit cat-calming pheromones which are only detectable by cats and have no scent to humans. Here is more information:
Try feeding all the cats some food from your hand or treats, together. Cats associate food with love and it's a pleasurable experience, so if Daisy can relate that good feeling to the other cats, as she's eating something yummy, it will help.
Remember, take things very slowly and try a little bit, each day to get them more used to each other with some of the methods I've suggested. It might take a little while, but, hopefully, they will eventually 'tolerate' each other--they don't have to be 'best friends,' but just exist peacefully, under the same roof.
I hope all goes well, and please keep me updated, if you can, on how things are going. Thanks!
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