"Neil can't read the writing, why do you think he would know what this beast is?"

The idea that Neil would know something isn't exactly wrong, he had been married to Elias, but if he knew of Dr. Coldwood's involvement with Nyarly then he likely would have said something.

"If he knew about this, he would have told us. Unless you think he's been lying this whole time?"

The flippant way she says the last part implies she's not going to entertain the idea.

"We'll go now."

Luckily she has Revelations with her today so there's no need to stop and get it before heading to the lighthouse.