Daren Kagasoff, Shailene Woodley Daren Kagasoff, Shailene Woodley

When Shailene Woodley was cast in ABC Family's The Secret Life of the American Teenager, little did she know she's spend a quarter of her life filming the series.

"When I signed on, I didn't think about award shows, magazines, the amount of episodes, but to get this far and accomplish 100, it's crazy to wrap your head around," Woodley tells TVGuide.com. "The most exciting thing about it is that all of us have seen each other grow and have a lot of first experiences on the show. It's really special to have those kinds of people in your life."

Secret Life's Shailene Woodley: Amy and Ricky finally make a decision about the wedding

Currently in its fifth season, Secret Life's milestone 100th episode airs Monday and features a very special celebration. Since Amy (Woodley) and Ricky (Daren Kagasoff) decided to elope, their friends throw a party in honor of their nuptials. "There might be some dancing involved. There might be some singing involved — not from me! There's one act that's different from anything we've ever done on Secret life before." (Watch Amy's friends perform "Marry You" below.)

The hour also features a full circle moment when Amy's guidance counselor (Beverley Mitchell) asks her to mentor a new freshman student. Although Amy's hesitant to take on more responsibly outside of the classroom, she quickly learns why the two are a perfect fit. (See their introduction below.)

Looking back on all the show's episodes, the Golden Globe nominee says the landmark 100th might just be her favorite. "It felt like a big episode when we were filming it and it might've been the most fun to film," she says. "[I love] any episode where the whole cast is working because [we all] hang out, [people] bring guitars, and for me what makes an episode the best is thinking about the memories from shooting it."

Secret Life's 100th episode airs on Monday at 8/7c on ABC Family.