Man, that was the most stupid idea for someone who was seeking for "stay alive".
1 - Okay that she was sending him and his companions to the death anyway, but far from there, that way she would not be responsible for his death. (well, that before she fall in love with him)
2 - But if he managed to stay alive and go back to his family, she is doomed.
3 - If any of her terrible simblings intercept Cassis, she is doomed.
This is not a plan to stay safe, she is pushing it to a final confront against her family.
So, how can she be worried to "stay safe" if her final plan is fight and kill everybody around (specially Sion)?