On assist she should not be able to proc foresight off of her basic attack. I just played a game where she never dropped foresight the entire match because of assists and phasma leader skill, even...
Personally, I don't understand why anyone even runs her in arena. She almost never gets to attack once, let alone do any significant damage.
Just take her out first and you won't have any issues. There are sturdier attackers that I hate running into in the arena. Rey is not one of them. I specifically target people using her...