Is the person you know with this name a Hispanic-American? The pronunciation you describe who be close to the one in Spanish, and Ibis seems to be primarily a Hispanic name in the USA. I think it still comes from the name of the bird, however, whether it's Spanish or English.
Alondra, the Spanish word for "lark", has been very popular as a girls' name in Latin
America recently, and
Iris is also really common in the Spanish-speaking Caribbean, so it would be no surprise that Ibis would be taken up as a girls' name by Hispanic parents.