I think the whole grooming/CSA allegations are a pointless rabbit hole to go down right now. Even if you could prove the emails are real (as in an actual email) it doesn't mean anything
Get ready for an unpopular opinion!!
Given the recent absurd video made by some woman with a fake voice claiming her Bethelite cousin told her Lloyd was an undercover Watchtower mole, it proves absolutely people are crazy and stupid enough to just make shit up. So it's entirely possible this character Marko was a fraud and therefore so were the emails. Why hasn't someone found him if he's her cousin-in-law? It's easy enough to check via births and deaths if she even has a married, female cousin, for starters.
Mind you we do know Dijana is wont to share his infidelities with people around her....photos, screenshots etc. That's definitely her "MO" & it's something a lot of women wouldn't do.
Anyway there's no point pontificating when we'll never know unless the victim came forward as someone said already.