Maria Caliban wrote...
"It’s a Keeper’s job to remember, even the dangerous things."
"All spirits are dangerous. I understood that. I'm sorry that you didn't."
Yeah, Merril is lying. She might think she can handle the danger, but she knows it's dangerous.
Not really. Merrill knows the mirror
was dangerous because it was tainted. But she fixed that when she learned blood magic. She knows that dealing with Audacity isn't entirely safe, but she also knows that he's been trapped for centuries, will continue to be trapped for centuries, can only be freed by a powerful spell -- one that we're unsure if she even knew --, and that she has no intention of freeing him anyway.
She knew the mirror shard was dangerous, but she removed the danger. She knows dealing with spirits -- especially demons -- is dangerous. But the trick to dealing with demons is playing them before they play you, and that's something she tries to tell Hawke whenever he deals with demons.