What is the ruling on a woman wearing an abaya on her shoulder while praying, and how does one respond to someone who argues about this matter based on the difference of opinion among scholars?

If a woman covers her body with the prescribed Islamic dress, there is no objection to her wearing an abaya on her shoulders, whether in prayer or outside of it. However, if she does not cover her body and intends to suffice with an abaya on her shoulders, this is forbidden, because wearing an abaya defines the woman's body, and thus does not achieve the prescribed Islamic covering. This may become forbidden in the presence of non-mahram men.

The second prohibition is imitating men.