A newer video from the other thread for some context:
https://www.washingtonpost.com/investigations/2021/01/08/ashli-babbitt-shooting-video-capitol/
The barricaded door was the last barrier between the mob and congressmen. The mob was determined to get inside, and once one person got through, everyone else would have felt confident of getting through themselves.
The police around the mob seemed completely overwhelmed and incapable of stopping them in any way. Even after cops with riot gear arrived, the mob continued to attack the barricade unopposed. No one went to stop the woman from entering a space where congressmen were still in the process of being evacuated.