Upon answering the telephone, the person calling asks if joan is available. If joan is the person who answered the phone, should she say this is her or this is she? So my question is should she has be contracted as she 's in the above example like in the examples found from google ngram to avoid confusion?

According to grammar rules, it should be this is she, because is is a linking verb (a verb that connects the subject to more information about the subject), so it can't have an object (her), but it's. She was in on the drama when the conman showed up at the stage door. If you are an actor in something, it's in: She was in cat on a hot tin roof. She was in the movie cat on a hot tin roof.

She was in the movie cat on a hot tin roof.