What if hen stops being broody?

[Nugget]

When I realized I lost the egg I was trying to hatch in my makeshift incubator a week ago, I put 2 eggs under by broody australorp. She had been broody for about a week prior and I'd previously been trying to see if I could stop it by taking her outside for free ranging and even taking her into my house once (she stopped laying, and she's my best). Each time she went back into her deep egg trance. Today she's off the nest. Maybe I'm overreacting... it's only been 20 minutes, but she was oustide, stretching her legs and scratching the dirt like I haven't seen since she became broody. I heard an awful ruckus in the coop before this. She's lowest on the pecking order and the others often don't let her feed. I let her back inside and locked the others out of the coop.

Will hens simply stop sitting? At what point should I set (a better) incubator up and take them from her? They are both viable.

 

[Nugget]

False alarm... to some extent anyways. She is back on the nest.
However if this had gone on longer, how long would you give it before intervening?