On Level 2 of Vault 13, talk to any of the upset vault dwellers. Mention that the quest is not going well. The citizen will then mention that there is a movement to leave the vault. They will then tell the Vault Dweller that the faction's meetings take place at 17:00 in Theresa's room.
Theresa can be confronted at any time. Convincing her to remain in Vault 13 requires an Intelligence of 6 and a Speech check and there is only one chance to do so, so saving beforehand is recommended.