Hey Holly
It all depends how small a one bed room we are talking. If its a Manhattan one bedroom I say crazy. kidding

I am assuming this response is for you and not a general question,

I don't see size being a factor with Mystic's size, however Mystic being 9 mths will probably be very territorial and all about her space, a puppy will not understand this, so you should at least be able to have clear separate areas for them to start. You don't want mystic being jealous and fighting for your love by beating the baby. I don't know how much beating up she will do at her petite size but she will try .

Then the other thing is the first meeting, I say if you are getting the dog from a breeder you should take mystic to visit the dog there, or bring home something with dogs scent, so Mystic kinda warms up.

* boy is your cat going to be upset,