‘Grish-ka Ot-re-pyev — anathema!’
I seriously interpret that whole interaction to be her madness. It's clear to me why she characterised the old Stavrogin as a Prince but not this one. It lines up with what Pyotr later says: 'I made you up myself abroad,' after his disappointment at Nikolay refusing him. Makes sense too becase Nikolay got married to Marya at around the same time Pyotr 'made [him] up'. And remember his conversation with Shatov: Nikolay had such revolutionist ideas two years ago abroad but now he does not, coming to nihilism - so Marya calling this Nikolay an owl is befitting.
