The 43-year-old actress discussed the new season and her experience working with Streep during Wednesday's episode of Good Morning America.
Witherspoon plays Madeline Mackenzie in the HBO series. Streep will debut as Mary Louise Wright, the mother of Celeste Wright's (Nicole Kidman) late husband, Perry Wright (Alexander Skarsgard), in Season 2.
The new season opens in the aftermath of Perry's death. Trailers have shown Mary Louise questioning Madeline and the other women about her son's demise.
"Definitely there's quite a few scenes where we take each other on and we have words," Witherspoon teased. "As my southern grandma used to say, 'We had words.'"
Witherspoon said working with Streep, a three-time Academy Award winner, was an overwhelming experience.
"The first day of the second season, I had to work with Meryl Streep," the star said. "Which is so exciting but also completely terrifying. I think I barely got out words."
"I had to literally go into another room and go, 'Calm down. She's just a person. She's just a human being,'" she shared. "She's just so amazing. And she's just so self-effacing and lovely and humble."