I definitely appreciate your dilemma, and I respect your decision.
The only thing I would counsel is to not let her get too invested in you before you tell her. If she is someone you care about, you wouldn't want to hurt her, would you?
Please check out The Birdcage - an open, friendly Polyamory forum for all parts of New York State
"Listen, or your tongue will make you deaf." - Native American Proverb