...she's probably 30-something, and rather hip.
I don't think many people could pull
Myrna off, but if you gave your potential girl a middle name that she could use as an alternate, then if she ended up not liking it or not fitting it, she would have a different name to fall back on.
Myrna Sophia is a little sing-songy, in my opinion.
I like
Myrna Jane, but it might be considered a little so-so, since
Jane is so often used as a filler mn. (I love
Jane, personally.)
What about..
Myrna SianMyrna JeanetteMyrna IsoldeMyrna Marie (another filler mn)
Myrna MarietteMyrna Marine (it's a little...rhymey, but I like it)
Myrna Maeve