After cutting off Sofie's arm defeating the Crazy 88, the Bride announces (from memory): "Those of you who are still alive and wish to keep their remaining limbs, piss off! Except you, Sofie! Stay were you are!"
Why would Sofie obey? She has a pretty good chance of hiding (or maybe, you know, finding someone with a gun). The Bride is essentially a stranger in Tokyo who just somehow knew about the Blue Leaves. Sofie on the other hand probably knows the city inside out.
Why wouldn't she obey a highly skilled killer? She knows The Bride would hunt her down and capture her if she fled. At least now she has a chance at survival.
https://killbill.fandom.com/wiki/Sofie_Fatale#House_of_Blue_Leaves_Massacre
A person in her situation wouldn't be able to think logically. She wouldn't think about who has more knowledge of the city and how likely evading her in the following days will be. Moreover it is relevant how Sofie perceives The Bride: is she dangerous to her? Well, as she just cut off her arm, the answer is probably yes. This is sufficient to make Sofie comply with any demand - in the hope that by satisfying the demand no more harm would come to her - no matter how likely that is.
A person in her situation only tries to flee or hide if the chance of detection by the perpetrator is perceived as pretty low. Usually. These decisions are mainly driven by instincts and individual assessment of the situation. Therefore you cannot really predict how the victim would behave.
In conclusion, her behaviour is quite believable.
