You have done right! Welcome

Mixing scents, letting each cat see the other - all good.

It is early days. It may take several weeks before they are cuddling up together, or that may never happen but they will be OK with each other.

Missy sees the kitten as an intruder and is establishing that she is boss. Hissing and paw swatting is part of that - even now after 12 months my 3 do a bit of paw waving at each other (but no hissing).

Although I haven't done it, rubbing talc on to each makes each cat smell the same and might help.