Maralen of the Mornsong was a commander I tried for quite a while, I like playing a silly DoomsdayHellcarver Demon combo, which I wouldn't recommend as it was more convoluted than functional. Unfortunately, Mararlen's biggest issue is the table wide tutors and the influence other player will perceive from letting you and their other enemies tutor anything (also when the red player plays Stranglehold you all cry).
That all being said the best way to protect Maralen would be to make the game hard to play for your opponents. Put thing likes Ob Nixilis, Unshackled within as a relatively fast method for winning (13 life loss on each opponents turn is pretty harsh). Also running continuous discard effects like Necrogen Mists and Bottomless Pit will prevent anyone from building up with your tutor, especially if you also use cards like Mindslicer, Head Games, and Monomania (and Dark Deal).
That all being said the best way to protect Maralen would be to make the game hard to play for your opponents. Put thing likes Ob Nixilis, Unshackled within as a relatively fast method for winning (13 life loss on each opponents turn is pretty harsh). Also running continuous discard effects like Necrogen Mists and Bottomless Pit will prevent anyone from building up with your tutor, especially if you also use cards like Mindslicer, Head Games, and Monomania (and Dark Deal).
As for wincon you may find that pretty hard, without board wide protection, things like Skithiryx, the Blight Dragon and Blightsteel Colossus may be your best bet, because slower instant wins like Exquisite Blood + Sanguine Bond can be more easily countered by a quick naturalize tutor.