I traveled with my daughter when she was three months old.
It was a interesting trip.
First off, if you are traveling with a baby you will be allowed to take the breastmilk with you on the flight. I was worried about that so I called the airline and they told me that I would be allowed to take the milk if I was traveling with my daughter and it was in the diaper bag.
Since I was traveling with her I did not take more than three bottles since I knew I could always pump or feed her when needed.
Anyways, you need to follow the guidelines for breast milk storage. I would travel with a one day supply of frozen milk. Once frozen milk is thawed you need to use it within 24 hours. So take it with you frozen and let it thaw in the diaper bag (but wrap it in plastic bags, ziplocks or a waterproof wet bag).
Since you are going to be gone for two days, the rest of the milk needs to be fresh, not frozen. Freshly pumped milk is good for eight hours non-frigerated and it is good in the frig for 5-7 days. So I would take day two milk fresh, not frozen.
Make sure you label the bottles of milk (like day one and day two) so your parents know to use the frozen first. I like using grease pencils (also sometimes called China markers).
While at the airport, you can pump (or breastfeed). Make sure you bring extra batteries/empty bottles. If you have time, try and find the "family bathroom" instead of the regular bathroom for pumping. There is always a plug in the family bathrooms and they have more room and are more private because they have a door and everything instead of just a stall.
Since I traveled with my daughter, I did not need to take more than I thought she would eat on the plane (because I did not want to nurse on the plane). I am also not sure if they will let you take what you pump (while you are away for two days) back on the plane when you go to get her. You will probably have to dump everything you pump while you are away. Since you won't be traveling with your daughter you might not fall under the "traveling with baby exception". To help minimize the amount you will have to dump. Get to the airport early (and be overdue to pump-engorged) and then once you are through security, find a bathroom to pump and then pump. That way you will at least have a bottle or two with you when you go to pick her up. Once pumped, it will stay ok out of the frig for 8 hours so you will have time to use it.
Good luck and remember, you can do this...