What would be the best line to ask her out again??

I want to ask this girl out but extremely casual nothing serious but I think she's the most finest girl I've ever met .What's a good line would you use to keep it just a simple acquaintance? I ask her out last Saturday but her mom is visiting.What's a good timetable to call her back again? Is email fine than calling? (Her phone has limited minutes because she's here temporarily)