[She was on Produce 101...][And she has been in 2 other girl groups before...]It's Kim Sohee!
Sohee ranked 15th in season 1 of Produce 101. She later went on to join temporary groups CIVA and IBI, made a solo debut with "Sobok Sobok" and "Sweet Potato x 100," and did various variety gigs.
[Breaking update: Gaga has left the group, leaving Nature with 9 members.]
Source: Naver (1, 2) via Kpopping (1, 2)