Re: Shia father and suni mother
She says so because her Father didn’t tell her Mother (husband not telling a wife).
She and the guy both are of same belief and know each detail.
Wedding is between a girl and a boy not between a boy and girl’s family or vice versa. Leave shia suni for a while and take muslim girl and reverted muslim boy then we say it’s not necessary.
Rather than imposing a fatwa of Munafiq, read and advice as I’m sure you know what islam says about giving an advice too.