Pattison and Guarnaccio got engaged while filming the MTV reality show's summer Chaos In Cancun specials earlier this year.
"We find out when we were over there. We were shocked, but we did kind of expect it to happen," Hagan told Digital Spy.
"Ricci is serious and Vicky is strong-minded. She wouldn't do it if she wasn't sure."
When asked whether she thought the couple would make it down the aisle, she added: "Yeah, I think they'll definitely get there. But they're being sensible and taking their time. They haven't known each other or lived together for long.
"Just because you get engaged to someone doesn't mean you have to get married these days. People are engaged for 20 to 30 years. There's no rush."
Hagan joked: "I think the first thing that I said was, 'What's the bridesmaid dress going to be like?'
"It will be an amazing wedding and the hen night will be off the scale. It will last for days and days and days. It will be one big wild session."
Watch our video interview with the Geordie Shore girls about Chaos In Cancun below:
Geordie Shore: Chaos In Cancun starts at 10pm tonight (June 26) on MTV.