"My aunt is by herself."
Translation:Mi tía está sola.
There are some situations were ES would be OK in this phrase. Without a context, we are lost here. Does teh sentences mean she is a widow? Or does it mean that for the next five minutes her 10 kids are playing outside? Using estar means the later; using SER may imply the former.
I'm sorry Talca, but I've never heard "Mi tia ES sola", that is not grammatically correct. Sola is considered a state not a caracteristic, so the proper use is with estar, the context is not relevant here. You would say, "mi tia vive sola" if you want to changr the meaning.