The sister's repeated jabs at the OP's career choice created a hostile environment. The OP was justified in removing herself from a situation where she felt mocked and demeaned, especially when her attempts to address the issue were dismissed. It is unreasonable to expect someone to endure constant ridicule on a day meant for celebration.
While the sister's comments were insensitive, leaving the birthday dinner was an overreaction that shifted focus from the mother to the OP. The OP should have found a way to address the situation without disrupting the celebration. Her actions made her the center of attention and overshadowed her mother's special day.
The sister was inconsiderate and disrespectful towards OP's career choice. While OP may have overreacted by leaving, the sister's persistent comments created an uncomfortable atmosphere. OP's actions were a direct response to the sister's provocation, making the sister primarily responsible for the ruined evening. However, OP could have handled the situation better by speaking with her sister privately instead of leaving abruptly.