Just because she can't speak doesn't automatically mean she doesn't understand. You just need to find an alternate way to communicate, learn to listen with more than just your ears: body language, posture, the sounds she makes when happy or upset. It'll require time and hard work but it isn't impossible.

[He gestures to where the Light Dragon disappeared.]

And before you ask, I'm quite certain she understands what we say. After all, she is you. If anything, I imagine it's quite frustrating to want to speak but be unable to do so. Whomever she wishes to speak to, she needs them to pay very close attention in order to share a message.

[His smile remains in place but his eyes are sad.]

She's likely incredibly lonely as a result of having so much she wishes to say but no one to listen.