I've matched with either a half sibling\aunt or niece on MyHeritage - we chatted and it seems like we share the same father. However, I have links to a 1st cousin once removed or second cousin, for her it's 1st cousin twice removed or 2ns cousin once removed. Likewise a match where I am 2nd cousin or 2nd cousin once removed and she is 3rd-5th cousin. I am also nearly 50% english ethnicity and 36% northand west european and she is only 16% english and 0% north and west european. She's 61% irish\scottish\welsh and I'm 0%.
It would seem to me she is more likely an aunt or niece based on this information - but the stories we have suggest she's my half sister so it's pretty confusing!