"Wald" is the place where the Fräulein is living or comes from.
Wald could be considered as the adjective melted together with the noun.
The accent in German is the same as in English use. The emphasis is on the part of the term that wants to emphasize the difference to others combinations with this noun.
Compare with non composite terms:strong text
Street-worker, a Englishman, Swiss-people (an accent on Englishwoman would make clear that it is an female not male.
Usually the nouns with the diminutive -lein are pronounced with the same emphasis as without diminutive.
Fräulein has an accent on the first syllable. But combined with Wald this emphasis on Fräu is lacking.
For once : as the ending "-lein" is a diminutive the accent might be there to emphasize that something or someone (the noun) is very small or little. e.g. the mother tells the little child who took a big piece of the cake: "Ich habe dir gesagt, ein Stücklein, not a whole piece!" (in this case the emphasis might be even on both syllables. (But keep in mind: This was still "ein Kindlein", a very little child.
In the diminutive of Frau this difference would never make sense as Fräu
alone doesn't exist. (In Bernese German we could do it as we say Frou and could emphasize to show it is a little girl: Froueli. But this would mean something different again, as the meaning of Fräulein or in our speaking Frolein or Frölein used to be not married of virgin.
However this difference will not be made with the other diminutive "-chen".
"Schau mal, ein Fisch!" - "Ach, das ist bloss ein Fischlein!" but no
("Ach was, das ist nur ein Fischchen!!)
So the Waldfräulein is the virgin of the wood with emphasis of wood and not virgin!