Having Marans myself I have a fairly good idea of how big Brownie is. I also have orps who lay large eggs. 10 eggs will be no problem for her to cover at all. She will also have no problem especially with warmer temps coming keeping 10 chicks warm during the crucial time.
With your two options I would move Brownie and her nest bowl into the tent tomorrow. This will give you time to see if the change in location is going to set her off. Some hens will absolutely not take moving nest sites, some do. If she throws a fit, starts pacing and refusing to sit in the tent even giving her eggs in there at lockdown is a no go. If you do this in the morning you will know by tomorrow afternoon if she will accept it or not.
Now if it were me, I would be inclined to give all 10 eggs to her for her to hatch out in either location. If she stays in the tent, get her and those chicks back out to the flock at a little over a week old. Personally I only isolate or try to isolate for the first day or two. My girls will whip everyone over their chicks. Brownie will not allow the other hens to harass them.
If Brownie will not stay in the tent I would set up the cage in the coop and still let her have all 10 eggs. Again only keeping them separate for a few days. You want her and the chicks intermingling. The newness of the chicks will wear off for the others in a day or so and they will be established flock members. Allowing Brownie to rear them you are doing the chicks a favor. They will be integrated from day 1 and will not have to be integrated around 6 to 8 weeks old and be picked on with no protection or a buffer like a mother is.
Also as much as I love hand rearing chicks, I cannot deny that the mothers do a 100x better job then I can do. Broody raised chicks in my opinion grow faster, learn more and just in general know how to chicken better then hand reared ones.
There is one potential problem that may arise with Brownie having chicks and I'm surprised it is not already rearing it's head. Personally from my flock observations I think broodiness is contagious. I feel if you have individuals or breeds that are prone to go broody and you allow one to sit, it is not long before others get the same idea. It comes in waves in my flock. It is very rare that I only have 1 broody at a time, normally they are in pairs. Sometimes the other girls will go broody a week or two after the first group start sitting, and sometimes they will wait until the chicks hatch to be triggered.
Brownie will follow her eggs and sit where I stick them, that is how I got her from the wall mounted nest boxes into the bowl nest I made. So, I know for sure I can move her within the coop and she will tolerate that change. I don't know if she would handle being separated from the flock for certain. 
