If I were Oda, I'd place a small army guarding her..
Oda has been giving her soldiers as guards and for her own use since her time as the chief of five villages. Started off with a few hundred and now up to ten thousand in the battle with Takeda. Ten thousand is equal to Tokugawa's forces in that battle and he's a Daimyo. Her army even has a name, the Shizuko corps, and they do everything from policing Kyoto to guarding VIPs depending on where Shizuko is located at the time.
When Tokugawa sent his two retainers to her as guests and they started doing sumo, her Umamawari and a bunch of Oda soldiers appeared out of nowhere. That's proof that she is being guarded by her own army all the time.
But if you only see like 2 guards with her, you're gonna have to blame Shizuko for that. Knowing her, she definitely sent the majority of the soldiers for training or some other task.