It' a quote from TV drama Gentleman Jack S1E01, a historical drama, set in England during the first Industrial Revolution. Here are the lines:
A: She says they were engaged.
B: Did he know about...
A: Yes. She says so. She said he was gonna marry her as soon as they got back to halifax. Happen the gin'll work. She looks sick enough.
I find it strange to use the word "happen", as it certainly doesn't mean "to take place" here.