Keep it simple.
At this stage, the vocabulary we have learned thus far on Duolingo is limited.
So far, we have learned 'lana' is 'wool'.
We have not learned the translation for items that we measure in metres, i.e. ropes, thread, to name a few.
This exercise is for one to get used to words for measurements.
Thus, it is not necessary for Duolingo to spend time on the change or include the option for 'yarn' or any craft material terms to be accepted for the translation of 'lana'.
Focus on the lesson plan - measurements; focus on getting the pronunciation right and focus on the usage or sentence construction common for Italian ( not how one fancies it in English or otherwise ).
"A meter of wool" isn't exactly American English, despite the spelling. Go into an American craft supply shop and ask for "a meter of wool" and you'll likely get some confused looks from the staff. And in another Duo lesson, there was a sentence "Put the toy in the bin" which was supposed to mean "Put the toy in the garbage can". But if you said that to an American, they would assume you meant a storage receptacle and not a waste receptacle.
Like some of the other Duolingo users, I wonder if "lana" refers to wool yarn, or rather, wool cloth. I tried "She has a meter of wool yarn," and was marked wrong. The translation doesn't make sense in American English (although it's a perfectly fine sentence as far as syntax goes).
I agree-- a "meter of wool" makes no sense to an American unless you're talking about wool yarn, and not simply fur from a sheep. And even then, a meter, or yard, of wool, is hardly anything, not even an armspan of yarn, and you can't really do anything with that, except perhaps patch up a hole in a woolen garment.
In my opinion, this is another DL sentence that makes no sense. To me, the word "wool" brings a vision of the sheerings from a sheep. What is a meter of THAT? Is it a cubic meter? Is it some wool fibers that have been twisted into a thread a meter long? I long for more practical sentences.
EDIT March 6, 2019.
Since my original posting a year ago, I have seen the following expression: un vestito di stoffa di lana. That translates to a dress of wool cloth. (Stoffa means cloth or fabric.) So, DuoLingo's sentence would make more sense if it were changed to the following: Lei ha un metro di stoffa di lana.
in most parts of the world wool is used. In North America yarn is used, meaning a ball of yarn or a ball of wool that you knit with. In North America wool can be understood as is it of animal origin. Does it contain wool (as in Merino, alpaca llama etc). I had to learn this when came to North America. Am an avid knitter.