Easy one - she "dual classed", which means she STOPPED being a thief and continued her life as a mage - unlike MULTICLASS (anything other than humans) which can specialise in 2 or more classes e.g. - mage/thief
which means BOTH thief and mage levels will go up.
Still.............nalia's not bad, she has 80% find traps I think (that's pretty good)
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Greetings Mortals. My Name Is Wah, Arch Lich Wah.