What is the grammatical construction of the clause "Emotions that Maria had thought were buried deep enough ..."

Something in that should have upset Maria, but all she could
concentrate on was the pain and anguish that ravished her body. It was
like a silent demon had lay dormant inside of her and fed on all the
pain that had ever been inflicted on her and those she holds most
dear. A demon that knew how to bide its time and unleash its festering
anger on anyone that was responsible for its creation. Was the inner
demon part of Maria? Or was it separate and just used the woman’s body
as a place to hibernate? Only Maria could answer those questions, and
she was in no condition to consider them. So many emotions fed that
silent demon. Emotions that Maria had thought were buried deep
enough so they could not betray her at the worst possible moment.

"Emotions that Maria had thought were buried deep enough so they could not betray her at the worst possible moment."

Is Emotions the object of thought? But how do you just "think" emotions? It is ungrammatical.

Or perhaps, that Maria had thought were buried deep enough is just a relative clause modifying Emotions? But this is also ungrammatical, there’s no main clause in the sentence now. Is the original sentence grammatically correct in the first place?