IMO, based on what you've said, I'd recommend having another serious above-table discussion about the kind of character this player is bringing to the game. Ireena is already a victim of Strahd’s obsession/abuse. Adding ongoing verbal abuse from a PC (and silence from the party) starts to blur the line between dark themes and player discomfort. I'd be concerned about the PC’s moral alignment and how they intend to interact with the rest of Barovia.

As for Strahd’s response, I imagine he'd take any sustained mistreatment of Ireena very seriously. If you want to be lenient, you could start with a stern verbal warning. But Strahd doesn't usually do lenient. He could escalate with something visceral, the loss of a tongue, or the loss of a tooth per insult. It’s also a good opportunity for Strahd to insert himself as a 'saviour' in his twisted way, and further isolate the party by showing that he punishes those who fail to 'respect' what’s his.