Went for spontaneous dinner with dsis and friend - they have met before and got on. I was supposed to just see dsis the friend asked if she could come for drink and hoped this would all be fine. Friend was friendly enough but can be cold/standoffish when she's doesn't know someone and this can come across as rudeness... I was making big effort but she was mainly talking at me and not dsis and it got a bit awkward. Dsis made her excuses to leave after an hour or so, but did leave earlier than she normally would have. Aibu to feel guilty?
No, of course you're not unreasonable to feel guilty because you're probably right that your sister was a bit miffed. Call her to explain the situation and offer to take her out again, just the two of you. How old are you OP? You posted the other day about having a row with your flat mates. Did that resolve itself?