Crackpot ACOTAR theory: Feyre is a descendant of an old, powerful faerie bloodline. OR, Feyre is the reincarnation of an ancient faerie. Sounds ridiculous, right? Just bear with me.

• For starters, there was the scene where Amarantha, a faerie who’d been around for a very long time, first learned of Feyre’s name.  “Feyre. An old name―from our earlier dialects.”  Maas wouldn’t just throw that in unintentionally.
• Before even meeting Amarantha, or any other High-Fae, Feyre dreamt of someone murdering her while asking for her identity. “My dreams had been filled with […] a pale, faceless woman dragging her bloodred nails across my throat, splitting me open bit by bit. She kept asking for my name, but every time I tried to speak, my blood bubbled out of the shallow wounds on my neck, choking me.”
• Nesta, Feyre’s sister by blood, was able to resist Tamlin’s glamour without using any relics (ie. iron, ashwood etc). “Apparently an iron will is all it takes to keep a glamour from digging in.” Or apparently their bloodline is immune to certain faerie powers because they too host those abilities.
• And let’s suppose Feyre’s ancestor was a High-Fae but did something so awful that the other faeries stripped him/her of his/her faerie body (like what happened to Feyre’s mortal body, but in reverse) and sent them south of the boarder.
• Once Feyre claims her High-Fae body, this scene happens shortly after… He bowed at the waist, those wings vanishing entirely, and had begun to fade into the nearest shadow when he went rigid. His eyes locked on mine, wide and wild, and his nostrils flared. Shock-pure shock flashed across his features at whatever he saw on my face, and he actually stumbled back a step. Actually stumbled. “What is―” I began. He disappeared―simply disappeared, not a shadow in sight- into the crisp air. He saw that ancient power being reclaimed.