If frozen milk loses any of its immunologic properties?

The reason I ask is - my daughter came home at 10-11 months old and never learned to nurse at the breast. She drinks her momma's milk from a cup. I have been pumping for 7 months now and am ready to slowly wean. However, Helina just started day care and I've heard it takes about 3 months for the child's immune system to adapt to those new exposures. I have some milk in the freezer that she'll get while I am weaning and was wondering if it will provide her any immunologic benefit. My plan is to gradually wean over the next 2 months and then give her the frozen stuff until it's gone. I know in Sep when school starts again all the minor illnesses will be making their rounds through day care, too, and that is about when she will be getting the frozen milk.