The actress, who plays Erin Silver in the series, claimed that she barely recognised the programme when she resumed work on the second run.
"This season is completely different," she explained in a behind-the-scenes video posted on the show's website.
"On day one, I said I couldn't believe I was working on this show because it is such a drastic difference, even from last year.
"We were shooting outdoors so much, which changes the show in my opinion because it's much more California. We were in sunlight, in bathing suits, swimming."
She added: "Even the friendships have changed. I've hardly seen Shenae Grimes (Annie Wilson) at all! Her character has gone off in a whole different wave than the rest of us.
"My best friends this year are Naomi (AnnaLynne McCord) and Adrianna (Jessica Lowndes)."
The new season of 90210 premieres tonight on The CW.