Have her dress in "friendly" looking clothes, and have her give friendly introductions and socials. If she says nice things, then, other Sims will think that she's nice. For example, the hermit in Granite Falls has the "insane" trait, and he or she doesn't scare other Sims.
Does your Sim have a job --- like tech guru --- I have genius tech gurus without the insane trait ---- or music, painting or writing could be good for a genius/perfectionist.