I'm not sure that's her reasoning.So I think this was kinda one of Aya's healthier life choices. In that she recognized that a relationship with Yuu is a sinkhole where he enables all her worst behavior (even here by offering to be a fallback if she won't do the hard thing of talking to Hikari) so she's like nope, not doing that again even though he gives her some momentary highs.
Although, to be fair, I can't comprehend her reasoning either way. Novel version doesn't help much. It's not like it's out of character, but I can't even imagine the line of thinking in those few seconds marked with "..."
I desperately hold back the sobs threatening to escape through my clenched teeth.
I force my trembling shoulders, my trembling legs, to stay still with every ounce of strength I have.
Even so, I can't stop the joy welling up from the depths of my heart.
You're saying... it's okay for me to sink into the evening twilight once more?
Me?
Me, who clouded the light... who even ran away from dusk itself?
You're saying... I can have Yuu...?
...
...
Maybe only a few seconds passed.
But inside my heart, it felt like an eternity.
At last, I managed to lift my eyes—eyes from which no more tears were falling—and look at him.
"Yuu..."
"Yeah."
There's nothing left for me to hide anymore.
I can't lie about how I feel.