It just depended on how much of a potential risk Ash believed there to be.
If it were someone believed to be highly dangerous, then it would be more likely that those watching over her would have to be just as strong and capable as her or even more than that.
If Ash tried to resist or escape at any time, then there needed to be a person or people who would be able to handle her if it was required of them.
There was always a possibility that she could be underestimated for being female and that she could use that to her advantage to slip past those guarding her or to knock them out when they had their guard lowered.
It was possible that her strength and capabilities could not be fully understood, resulting in those watching over her not being enough to handle her resulting in she was able to do the same without using any tricks or them underestimating her.
If Ash had betrayed Cerberus or if there was anything else wrong, then she could not be allowed to escape.
