Strong Faerie Blood suggests part of your appearance matches your Faerie source - eg blue blood, eyes, teeth, ears, etc.
How extreme can this get?
eg animal heads, or extra fingers, joints or limbs, etc.
There are so many triple goddesses, where is the polycephaly?
Mermaids and Melusine.
Dragon or troll blood?
Strong Faerie Blood by itself does not normally include extreme enough appearance that people automatically react negatively to it. RoP:F p106-110 contains many examples of typical appearance options for various faerie blood types.
If you look really weird you probably have the Monstrous Appearance flaw (RoP:F p52 and p107)
Another option (but mainly for characters associated with the Magic realm rather than Faerie) is the Horrifying Appearance flaw (See Rival Magic p83, and The Sundered Eagle p120) or Monstrous Blood (RoP:M p49-50)
The Repellent flaw (RoP:I p89) is also a possibilty, but that is mainly associated with the infernal.
Pretty extreme, I suspect, but at some point the appearance goes from 'uncanny valley' to 'freak' or 'monster' and dark paths are followed by adults and children.
A player in my saga which just ended had antlers and long ears (like a deer, not an elf). No monstrous appearance Flaw in her case because the culture she was a part of approved of faerie blood.
Lots of lonely Norse giantess, that’ll give you a nice run of giant blood or from tCI you could have a fomoir half blood, that’s going to get all sorts of horrific appearances.