Congratulations to your daughter -- How exciting!!! When we set up connections in Athens - transferring on a separate ticket with checked bags - we always allow 3+ hours. Given that YOU HAVE TO BE THERE for this event, I'd plan on an overnight stay at the Athens Airport (The Sofitel Athens Airport has a great wellness spa - make it a spa day and recover from jetlag!).
Because you have a checked bag, you would have to land on time, exit the plane, head to immigration, clear passport control, go to the baggage carousel, wait for and retrieve your checked bags, exit security, find the check-in counter for your next flight, drop your checked bag off, go back through security, then walk to your gate... in less than 1.5 hours. That seems to be a tall order in Athens, based on my experiences there. And if you're on separate tickets, you'd be "unprotected" on that second flight, so then buying a next-day ticket could get expensive. (And what's your recourse if that "next" flight is SOLD OUT?). And given the number of changes airlines are making in schedules --- what if the arrival time for your first flight changes, creating an even narrower window?
There are just too many factors out of your control like... arriving on time in Athens, the length of the lines or # of open counters in immigration, or how long it takes for your checked bag to show up, and even the first airline changing your arrival time. I suppose you could use a company like Luggage Forward and send your checked bags on ahead of you. It MIGHT be doable with carry-on only, but for the cost of a pre-shipped luggage company - and still not knowing for sure you'd make it because your first flight was late on a day YOU HAVE TO BE THERE - I'd spend that money on a spa day, relax, and arrive at the wedding site rested... and not stressed out.