"She went through a lot last year," they explained. "Amber wasn't in the best frame of mind."
Portwood, who gave birth to son James with boyfriend Andrew Glennon in May, admitted in the season finale that she had contemplated killing herself after dealing with postpartum depression.
"She did her best to show up to work and do her job," the source said of her decision to film amid her mental health issues. "She didn't want to disappoint the fans and the crew so she did her best. She gets along well with the crew and has worked with some of them for 10 years, they are like family."
After declaring in the Tell-All special that she was done with the show by tweeting, "The heartache this show has put me through is too much to bear anymore," Portwood has decided to continue appearing on Teen Mom OG, with the source claiming filming is currently "in the works."
"She's excited for the new season," the insider said. "She's doing really well and feeling better. She cares so much about everyone."
Despite her clashes with production and crew members last season over what she saw as preferential treatment for co-star Catelynn Lowell, whom she claimed was allowed more time off for her own mental health treatment last year than she was allowed after giving birth to her son, the source added, "She's definitely not a diva. She thinks of the crew like her family, they see her on the best and worst days."
As for her decision to return to the MTV show for a ninth season, a source previously told the publication, "She had second thoughts about leaving. She now wants to stay with the MTV family and share her story. Because of the fans, and her 10-year history on the show, she doesn't want to leave abruptly."
Currently, Portwood is spending time with her family after getting into a fight with Teen Mom 2 star Jenelle Evans, whose husband Portwood called a "clown" on Twitter. After Evans clapped back, telling her co-star to "shut the f— up," Portwood went on a heated rant about the controversial reality personality, threatening to "beat" her and warning her to have security.
"It's a beautiful new day!!" she tweeted soon after. "I just want to thank everyone who has helped me understand that I should be above situations and turn all my negative energy into positive energy!! Sending so much love everyone [beautiful souls]."
Teen Mom 2 airs Mondays at 9 p.m. ET on MTV.
Photo credit: Getty / Alberto E. Rodriguez