Are they fighting or learning to love?

Hey all,
I have 2 cats. Dora I had since she was a kitten now she is just over one year old. I saw her playing with cats outside all the time so got her a sister Ivy to play with. She is 9 months and has been in the house for about 6 weeks.
Dora hated her. I think she still does in a way. The cuddles stopped and the normal happy cat personalits seemEd to go. Over the 6 weeks it has got better but ivy keeps jumping and biting Dora's neck. There are squeals and I break it up. Dora is now fighting back which is making the fighting frequent and more bouncy and full on. There are squeeks and squeals but no fluffy tails, no hissing. It usually begins with the kitten going towards Dora locking her head then in for the neck, can't tell if they are fighting or playing. I have feliway on now at night for calm time which works. I am concerned as I don't want the older cat being miserable all the time. She goes out all day and gets lots of attention when she is home.

Reads like rough play to me. It's also likely that Dora's other cat friends are not as rowdy as Ivy so she is not used to handling her but she is learning.   Ivy seems to be quite an overactive kitten. Take off some of that energy by tiring her out with play while Dora is out.