No. First in English you cannot use woman as an adjective - so even if the abomination mérnöknő was used you cannot say "woman engineer" but rather "female engineer" - then wait for the explosion (FYI I am a woman and an engineer)
But the Hungarian is clear. There is the woman (a nő) and an engineer (mérnök) so therefore the woman is an engineer.
Hungarian often avoids gender specific words, and many phrases can be rewritten to minimize gender specification. A woman would just be an engineer in common usage. There is no need for mernokno. Besides, how would you say mernokferfi? It's awkward and unnecessary. Gender doesn't add anything to the meaning of engineer, especially since it's already established that we're discussing a woman, earlier in the sentence.
You are not forbidden to say "A nő egy mérnök" if you want. I wouldn't say it would sound better but not wrong for sure. "A nő mérnök" (for "the lady engineer"), however, doesn't sound like something I'd ever want to say.
Though, if you are still not happy, intonation is a thing. :)