The depiction of hell as a literal lake of fire is scriptural. For example in Revelation 21:8: But as for the cowardly, the faithless, the polluted, as for murderers, fornicators, sorcerers, idolaters, and all liars, their lot shall be in the lake that burns with fire and sulphur, which is the second death.” One thing I have noticed in the authentic marian apparitions or those approved by the Church is that her reported message is scriptural, has its roots in Holy Scripture. Mary speaks the language of Holy Scripture, the word of God. In fact, Mary is the mother of the Word of God. Mary is not going to contradict the word of God. In fact, if some proposed apparition of Mary did contradict Holy Scripture, I think the authenticity of such apparition would be suspect and questionable.
The only knowledge we have about hell is what God has pleased to reveal to us in Holy Scripture. Fatima and the private revelations of various saints generally conform to the ‘picture’ or depiction of hell scripture gives us. Anything beyond scripture is pure speculation, imagination, and opinion.