Can you mix milk from two different pumpings?

I have always stored my frozen milk in 2-3 oz for easy thawing and perfect portions for rice cereal or baby oatmeal. I am going out on Friday (so excited) and want to know if my MIL can mix them to make a full bottle? I can't really pump more then 3 oz at a time, and I hate pumping so I usually stop after that.