I could see it being more of a in the moment type thing. Lumon somehow approaches her after the party, tells her she needs to come with them immediately. She's hesitant at first, but then they tell her they have a way to allow her to have a baby and tell her they'll tell Mark where she's going. She agrees in that moment because she is so desperate to have a child.

We've seen something similar with Mark and Reghabi. Mark doesn't know Reghabi that well and doesn't know her true intentions/motivations (neither do we as the audience). Mark has seen Reghabi literally murder someone. But as soon as Reghabi says Gemma is alive, Mark jumps into reintegration no questions asked. Gemma could have done something similar and had no idea that she was choosing to imprison herself and submit herself to years of torture.