My guess for the reason she is pissed is because the main character keeps putting everyone and the business before his own well-being. He helps out with the funeral of others, but hasn’t been able to hold his own parents’ funeral. She also wasn’t there in the hallway with the other construction workers when the office lady explains the main character’s reasoning for refusing his help (ch. 22), so she doesn’t understand his rationale like the others now do.
Also, I doubt that the main character thought that the interest was marrying the daughter - it’s probably just a dumb rumor to bring in misunderstandings/drama.