definatley you'll need to use a breast pump...formula isn't going to cut it...it's just not the same. try pumping your mild and feeding her from a bottle yourself ...using a nipple that most looks like a nipple. after she gets used to you doing this, then let the mother in law feed her while your there. see if she's doing it right. do this until your both comfortable. it's hard to have fun going out if your worried about your baby not eating! also...are you sure your mother in law WANTS you to go out...??? think about that too