if you know about tarantulas or have one please answer

ok so i got a rose haired tarântula from my science teacher and she has fed it one cricket per week and we went to the pet store and we got a dozen and were told that it would last her 1-2 months well it hasn't even been a 3 weeks and they are all gone so does that mean i need get her mais or do i just leave her alone because she is full