hmmm... could you request a trial basis perhaps?? Then, keep the newcomer in a separate room for a few days so that Marigold can get used to her scent - then try some gradual introductions?
You never know until you try. Ours have all been adults until our last few years with kittens. Each new adult was added to the household with no problems. I only know to pretty much ignore the newcomer and shower Marigold with lots of love.
Let us know what you decide!!