Thawing milk for the babysitter

So I go back to work in a week and I’m a FTM who is EBF. My son takes a bottle well with no nipple confusion. I have milk frozen and stored but my question is about what to send to the sitter. Should I send her frozen milk or prepared bottles? I’m not sure how much my son currently eats (oz) because I BF when I’m with him. Should I prepare a bottle to see how much he eats? I don’t want to send too much frozen and waste it but I also don’t know how long milk is good for frozen to fridge !

Photo for attention 😭