New Kitten and Resident Cat Don't Always Get Along?

I have been reading these posts looking for suggestions and such. I am currently fostering a 12wk old kitten who was found outside my sister's job, motionless, at about 5wks of age. It was severely dehydrated and anemic from fleas. She vetted her for the day and brought her to my house to foster, including bottle feeding, meds, you name it. Well now 2 months later she is a healthy, very energetic kitten who just wants to play.

I have a 3 year old female tortie, who is pretty laid back. I kept the kitten in a huge tent like pen for about 1 month, only letting them together when I was home. I think a month was sufficient. My older cat had access to sniff and smell all the time. Well now that they are not separated anymore, any time the kitten sees the older one, it's like WWF under my bed. My cat has no tolerance for her antics, and bear hugs, and biting of her tail, lol. My cat hisses, growls, meows, you name it and the little one just keeps pressing on. When it gets too much I redirect her with a toy and then separate. But other times, I will find them laying next to each other under my bed. I'm assuming this is all a normal part of "distinguishing boundaries"?

By Simi112671