Obi wan was a council member and a master but Yoda told him not to face sidious. The council should of sent jedi who have actually had experience fighting sith. I mean maul was the one who killed Qui Gon who was a better fighter than Adi. Also i wasnt trying to be sexist there are plenty of BA females in star wars i just dont consider Adi one of them.
Sidious would have destroyed Obi-Wan. Obi-Wan wasn't strong enough and Yoda knew that. Adi Gallia was a member of the Council (senior member) and they assumed that she could handle herself. But they hadn't realized how powerful Maul had gotten. Hence, her death.