When a righteous woman passes away what is the appropriate term to use to indicate "in her blessed memory"?, i.e., is there a lady's alternative to z"l ?
I have seen Z"L used routinely for both men and women.
You ask what's appropriate. I don't see why z"l (or ז״ל) would be inappropriate. Nonetheless, I have often seen a"h (or ע״ה) for a woman where the same text included z"l (or ז״ל) for a man.