Re: BF'ing 1 and EP'ing for a 2nd?
OP, your offer is wonderful. I have donated a lot, but like everyone else, my life is too hectic a lot of the time to pump at every feeding while also nursing and caring for my children. This is not an easy road you're going down if you don't have to to feed your baby.
Has your SIL gotten good quality help from an IBCLC? That her doctor said her milk doesn't have enough calories is a huge red flag for bad breastfeeding information. That's not what people who know breastfeeding would say.
Catherine, tandem nursing mama to Preschooler Girl 9/08 and Toddler Boy 3/11
Breastfeeding for 4 years and counting!