I have been praying for your sister. Being an adoptive mom my heart really goes out to her.
Has she identified a family with which to place her baby? Is she using an adoption agency or is she going private?
From what I understand, birthmothers hate the phrase "giving the baby up" as 99.9% of them really don't want to place their child for adoption...they really want to parent them no matter the circumstances of their pregnancy. Just an FYI to help when you're communicating with your sister.
After she places her baby...let her talk and ALWAYS honor her sadness, remember the baby's birthday each year and take her to lunch if needed. Just love her through this...it's a very sad time for her right now.
I think it is wonderful that she chose to give this baby life...it was a very selfless act.