I have always had multiple cats, two sets of sisters and then one my husband picked up.
The two sets of sista's
always slept with each other, really bonded to each other..Funny to note,,the first two, 1 I had to pts last year, she was 20+ years old,,her sister, was always the peace maker, she got along with everyone, when her sister passed, she hooked up with one of the other sista's who are 9 years old..
Now she has passed
So I have two that are 9 years old, and they are best buddies, the 'loner', has hooked up with Masi, which is totally hilarious..
So to stop rambling, I do think cats benefit from being "two",,however, some don't get along with newcomers, but then some do..
I'd try fostering and see how that goes, and maybe become a foster failure..
I'll bet it's really cute tho that she's smoozing up to the ferret,,do you think you could let them be together, supervised of course???