You have the right to feel hurt about this situation. I'd feel the same way.
What stands out to me is that you stated.. "I've mostly" patched things up with my sister. Apparently, things are not patched up or she wouldn't be crossing your boundaries, which is what she's doing.
My advice...don't let it bother you. Maybe that's what your sister wants. Continue making conversation with your friend and treat her like you've always done. Let her be friends with your sister w/o taking offense to it. However, if this continues to bother you, talk to your sister about patching things up all the way.
In the meantime, go about your daily business and focus on other things to make you happy.