jiahan

My mom came to USA to visit me via B1 visa. But recently we couldn't find her I-94 card. Actully I never saw that she had it this time (she ever came to USA before). I just confused if she lost it or she dosen't need it every time. Now, I have two questions:
Question 1: If she ever had it and lost it, how should we do now?
Question 2: If the period she is allowed to stay in USA is printed on I-94 card? Because I really don't know when will she has to leave. She got the visa last September and the expired date of the visa is the beginning of September this year. She came to USA last September and stayed for 5 month then left, and in the middle of this April she came again with her valid visa. So, the question is she can stay here until the beginning of this September (according to the visa expiration date) or October (according to her second time entry day if she can stay here for another 6 month)? Or I have to look for the I-94 to see what's on it?
Thanks a lot ahead!