Only you are able to best gauge which is the best choice because only you are able to first hand scrutinise your home environment (both inside and outside the house), Ashley's adeptness for caution and self survival (climbing, watching out for traffic, evil 2 legged beings, etc, etc), just like a direct and physical examination done by the vet.

Based on my own experience with my cats (I have more than you, dear) your having 18 cooped up in the house is waaaaaay over-crowded for them even though they have the whole house to roam.

The grown ups especially need their own personal space and will tolerate one another and work out their own routines around each other. The ones who have never known freedom will be more accepting of the cooped up environment, but those that have known the outdoors will definitely have more stress, especially as they grow older. Cats may huddle and sleep together when young but do so more infrequently as they grow older and will prefer to maintain their individuality and personal space. This is what I have observed in my cats and understood through the explanations of the famed animal scientist Temple Grandin. I understand the animals better now and are better able to care for them, I'm so glad.

This is one of the reasons why even though spayed or neutered, some of the cats still urinate and mark areas with their urine. It is their way of insisting on their presence in the midst of so many. My Mandy had suddenly one day started urinating on the floor of her cage which is the upper partition since the day Bonnie (who lived in the partition below her) started bullying her when they were let out to play together. Till today, Mandy gives her a real dirty look of disdain and Bonnie looks at Mandy with real vengeance in her eyes and adamant to leap up to bite and scratch her! (Not play-play one!) And Mandy will always seek to creep up my lap and bury herself there for protection.

Well, seeing is believing ... and kalau orang cerita this kind of animosity in animals pun I tak caya ... thank God this is only one single incident of cat animosity (macam cara orang membenci pulak ...) in my whole experience with all my kids.

However, from the way you cerita and describe Ashley, my gut feel is that she is competent enough to be free, and will not wander off to leave you unless she has an unfortunate accident. But then, we are only stewards and one day, all of them will leave us. Outdoors (at least controlled outdoor environment with our watchful eyes always on them) is their natural environment and they need the freedom and stimulation and they need to be the cats that they are. Loving is being able to let go, dear, and Ashley will be a very happy girl.

However, what I say here applies specifically to Ashley alone, not the other cats that have not know outdoors because they lack the street-smartness of Ashley who had the opportunity to sekolah outdoors dulu.

That is why domestic pets suffer more and are more sick when abandoned by owners to live outside on their own compared with strays. They were deprived of the chance to sekolah and be street smart. They were also deprived of precious life lessons from their mothers - what can be eaten, what to ignore, what to watch out for, social skills, who to attack and who to run away from.

Hope this helps. I love dear Ashley.

p.s. ... and since you mention that she is a heights girl (she climbs) - no collars whatsover even an elastic one. Though they look cute and can serve identification purposes, none of my cats wear any for absolute safety. That one I take absolutely NO chances!