Unless she's constantly late (as a person), you would use 'estar' rather than 'ser' to express that somebody is running late for an appointment. In this case, when no 2nd pronoun is used (who/what is late?) and when 'ser' is being used, I don't think there is any doubt about the meaning... :-)
Agree, and generally I think we estrangeiros need to work on achar/pensar/crer, but in this case English "find" should be accepted since it's both literally and semantically meaning exactly the same as "acha" in PT. "He finds her attractive", "He finds it's time to go home" etc.