DD will be seeing her birth sister soon, we're hoping to have a good relationship with the family (she's adopted) and see a lot of them in the future.
My issue is that I'm wondering in the longer term what to call this little girl person and her family. Obviously we'll call her Ermintrude/Amanda/Persephone/whatever. But it occurs to me that DD will need something to grow up calling her so that it doesn't immediately 'out' her as adopted when someone at school asks what she did at the weekend - as in 'I saw my birth sister'.
DD also has a sister (our BC) so we don't want to use 'sister' as I think that confuses the nature of DD's relationship with DD1.
DD is only 15 months old so she doesn't have a word to reference this relationship. But DD1 is at school and I would prefer she wasn't using the phrase 'DD2's birth sister' to people there.
So do we go with something artificial like 'cousin' which doesn't feel right? Or something else? Any ideas?