Η θεία μου λέει ότι η σκηνή που της αρέσει πιο πολύ στο θέατρο είναι όταν όλοι τραγουδάνε μαζί.

My aunt says that the scene she likes most in the theatre is when everyone sings together.

Breakdown of Η θεία μου λέει ότι η σκηνή που της αρέσει πιο πολύ στο θέατρο είναι όταν όλοι τραγουδάνε μαζί.

• είμαι: to be
• μου: my
• μαζί: together
• σε: at

Questions & Answers about Η θεία μου λέει ότι η σκηνή που της αρέσει πιο πολύ στο θέατρο είναι όταν όλοι τραγουδάνε μαζί.

Why is it Η θεία μου and not η μου θεία for “my aunt”?

In Greek, the unstressed possessive pronouns (μου, σου, του, της, μας, σας, τους) normally come after the noun, not before it.

• η θεία μου = the aunt my → my aunt
• ο φίλος σου = the friend your → your friend

Putting μου before the noun (η μου θεία) is ungrammatical in modern Greek (except in some very old or poetic styles).
So the normal order is: article + noun + possessive pronoun.

What exactly does λέει ότι mean here, and how is ότι used?

λέει ότι means “(she) says that …”.

• λέει = she says
• ότι = that (conjunction introducing a clause)

So:
Η θεία μου λέει ότι… = My aunt says that…

A few points:

• ότι introduces a reported statement, like English that in She says that…
• You will also see πως used in the same way: λέει πως… ≈ λέει ότι…
• In everyday speech, ότι/πως is often dropped, just like in English:
  
  • Η θεία μου λέει η σκηνή… (colloquial) ≈ My aunt says (that) the scene…

In careful written Greek, ότι (or πως) is normally kept.

Why is it η σκηνή που της αρέσει instead of something like “η σκηνή που αυτή αρέσει” for “the scene she likes”?