Since the only
Mahalia I'm familiar with is
Mahalia Jackson, I pronounce the name as mah-HALE-yuh. I also know, though, that
Mahala (which was really much more common in the 19th century) was usually pronounced mah-HALE-uh in the USA at that time. There is a woman in my family tree named
Mahala who was called
Haley in everyday life, showing that
Haley can have another origin besides being an alternate spelling for
Hayley.
However, I think it would be OK for you to say mah-HALL-yuh if you want. It's a very rare name anyway, and most people under the age of 35 or so probably have never heard of
Mahalia Jackson.
I can easily picture a
Molly as you describe, but in either pronunciation it's a little harder to picture a
Mahalia that way. :)