This is Ava's wish

"Keep her here forever?"

Sam had heard similar words before, in a dream that belonged to Mia. That woman... Sam wasn't sure whether to call her Mia's inner demon or a negative personality. 

But that entity carried many of Mia's negative emotions, embodying the darkness and negativity from her entire life. The pain of losing her mother, the loneliness of being treated as an outcast, and all those moments that made her feel insignificant and unimportant.

The solution offered by this negative aspect of her was to replace her, to exist in a way that was stronger and more aligned with how others saw her, leaving the real Mia trapped in a dream forever.

Now, this 'Ava' was saying something similar.

But why keep Mia? Besides, it was their first meeting, and Ava's perceptiveness wouldn't likely have picked up on any intimate nuances between them so quickly. Even if she had, it was far less significant than with Angel.