bbm... I think this is the pertinent information. Le was not legally obligated to mirandize Casey because she was not deemed a suspect.
Yes, it is one of the factors. The Supreme Court has said that the controlling factor is "restraint on liberty" which basically means, you can't leave if you want to. Then before any questions are asked, you must be read your rights.
It all kind of works hand in hand. LE can't restrain you without probable cause and if they have probable cause, you are definitely a suspect.
Salem