Mr Kerr was the caretaker at Ms Miller's old school, Woodfarm High in East Renfrewshire.
Ms Kerr said:
"It's my dad and I'm 32 so imagine how me and my family feel seeing that? We have nothing to do with him anymore."
Other social media users have expressed their shock at the proposal, with another former Woodfarm pupil, Darren Law, sharing a photograph of the pair getting engaged alongside the caption:
"No chance. Hahaha. A girl in the year below me has got engaged to our school's janny. Fear."
In the video, Ms Miller can heard saying:
"Jim, we've been going out for just under a year and I love you so much. I wouldn't swap you for the world and, marry me?"
He then says, "Yes, definitely," before they share a passionate kiss.
Emotional teenager Ms Miller is then seen wiping away tears before cuddling her new fiance.