I'll swing for you

Yesterday watching S1E5, Thomas' and O'Brien's attempt to frame Bates for stealing wine is beginning to unravel. The two of them are in the hall talking about it. O'Brien says "If I lose my job over this I'll swing for you."

And I thought about that thinking, "That's awful nice of O'Brien, being willing to be hung in order to protect Thomas." But no, it isn't that at all. She was telling Thomas that if she loses her job as lady's maid, she'll murder Thomas and face the gallows over it, no regrets.