Eh. Cynthia is legitimately borderline retarded and is unable to function on her own. The biggest danger she poses is to herself and her family's money because she is a fool who is easily parted with said money and she has quite the vicious and unfriendly personality too. She's alienated her preferred wogglebug voice actor, thinks herself better than the other special education kids she had classes with, alienated perhaps her best chance at getting exposure for her little dream and finally was extremely vitriolic when talking about another wogglebug fan because they had a disagreement or something.
Sarah, were she properly medicated with a supportive family I can easily see as being independent and even having a fulfilling if not happy life. I'd rate Sarah far above Cynthia in terms of coziness, but a more unfortunate life.