I did mean to ask earlier, OP, whether you are i the UK, and if so which region?
Just that for some reason I imagined you were on some picturesque Alpine slope, and our RSPCA wouldn't be in the picture, nor would offers to rehome this kitten be possible (in the UK), if you couldn't give it a warm and welcoming environment, after the comments you had posted early on.
I am glad your husband appears to have accepted that his "not in the house, except to sit on laps" approach was wrong, but would like to see you confirm that this kitten is guaranteed the opportunity to stay indoors overnight and pretty much whenever she wants, and that the mid-afternoon situation was not a "one off".
You acknowledged you had no experience before, and at one point wished you had not brought this kitten home. You may have a fair amount of heartache as your kitten grows and gets adventurous (I think there's a Go Kat advert, also available on YouTube where some rather acrobatic (and possibly photo technique enhanced) young cats are running wild.
Well, in all truth, cats only learn not to do things when they can confirm a past attempt where they got hurt, so do expect some wild climbing and random acts of vandalism (hint, running up your curtains isn't just in the imagination, it might well happen) to take place, so do "give her a break", as many other cats like to "explore" too!
My somewhat elderly 12-ish year old climbs up the edge of the shed (one or two small panels are missing so she treats it like a ladder with large steps and small gaps) to get onto the roof of the garage. Not to catch birds but it appears she likes the view and it gets the sun from quite early in the morning (e 06:30 at present) and she is out of harms way.
Coming down is a bit more stressful for me, as she jumps down some 4 feet to the fence post tile (problem is one front leg quivers when she is sat on her hind legs, so I'm concerned it may give way one day instead of being her shock-absorber) and then another few foot to the ground...