Remote MacBook Pro reduces mic gain when I talk over FaceTime

My fiancée's retina MacBook Pro automatically severely reduce (not completely though) her microphone's gain whenever a sound (me speaking or some ambient noise) on my end is sent to her over FaceTime. Basically the audio from her that I hear from my speakers gets very quiet. For example, if my fiancée is talking about about her day, and I say "Ah, OK." as she continues to speak, I can barely hear what she continues to say until I am finished speaking as well.

Completely muting my own microphone stops the issue from occurring.

This issue does not affect her previous MacBook. We can immediately change to use her previous computer to call me, we can talk at the exact same time, and I still hear her at full volume as when I am being silent.

Disabling or enabling "Use ambient noise reduction" on either of our computers does nothing to change the problem.

If she plugs in her Apple earphones to use the microphone and speakers on that, we can talk at the exact same time, and I still hear her at full volume as when I am being silent.

This leads me to believe that the problem lies with her computer, not mine and not the Internet connection being too slow. This also leads me to believe that there is something wrong with her microphone (or software running the microphone) on her MacBook Pro. It seems to be too aggressive in reducing the microphone gain so I don't hear myself from her computer's speakers. While yes, I appreciate not having to hear myself, it worked perfectly with her old computer as I stated above.

Continuing to use her previous computer is not a valid solution. How do I fix this?