post surgery

My two female cats have lived together for a year and the youngest was just spayed yesterday. My other cat (Presto) is curious about why her friend (Bumble) is so lethargic, and has also started hissing and growling- but not attacking- she just keeps her distance. I think this is because Bumble smells differently and is behaving differently than she did yesterday. Tips? Will this go away?
Thanks!

You should keep them apart for at least a day anyway, but before you reintroduce them, take some pure vanilla extract and put some on each cat in three places, under their chins, between their shoulders and on the base their tails. Do this several times a day, it will neutralize the smell of the vet, the clinic and the medicines

You should be fine if you follow Hissy's advice.

When we had a precancerous tumor removed from our older cat Much, our kitten, Lucy, was totally confused at who this funny smelling stranger was. And then the poor thing was wandering around looking for her beloved Much. Lucy eventually came around and now torments Much just like before.