The 26-year-old actress started work on the fifth season of the show on Thursday, just two weeks after her boyfriend and co-star, Cory Monteith, died from a heroin and alcohol overdose at the Fairview Pacific Hotel in Vancouver.
She tweeted: "First day of glee today..And at my first wardrobe fitting for Rachel Berry for Season Five! I've missed her so much (sic)."
Meanwhile, it was recently revealed that Emmy producers are currently planning the best way to pay tribute to Cory at the awards ceremony, which will take place at the Nokia Theatre in Los Angeles on September 22.
Executive producer, Ken Ehrlich, said: "Something that reflects an homage [is being planned, but] what the extent of that is, or how we're going to approach it... well, it's too early to tell.
"If Cory had passed away in March, we'd have had four months to look at this with a little more perspective. The reason we're getting all of this discussion now is because he passed away two weeks ago. But we are going to deal with it."