It means: "She agrees with what is being proposed. She is not against it." In this case "a" is not an article, it's a preposition.
The noun "favor" is masculine, the article would be "o favor".
Ela é a favor.
Ele é a favor
Eles são a favor.
Eu sou a favor....
We all agree.
Meh...this is a silly sentence. I though "It must be "E um favor...cause nothing else makes sence".
As Blue bird says "She is in favor" would mean "we like her" in English...For the other meaning we would say "She agrees with..." or "She is in favour of...."
Actually, I've often heard "she is in favor" to mean "she is for that" like in a formal meeting... "who is in favor? who is against?" At least that's true where I grew up in Pennsylvania (USA).
Some expressions has its own prepositions. It happens in every language. So it is 'a favor de' (in favour of)
Perhaps they need to add more to sentence to give it a better context. Like: Ela é a favor a nova regra?
In Portuguese this sentence makes sense by itself (just a small correction: ela é a favor da nova regra?)
While it can make sense in Portuguese by itself...it would be helpful to those learning, to use a better example to mitigate any confusion. :)
"a favor de".... I now will remember!!! Thanks!
Yes...it certainly wasn't the easiest to translate to English. It just didn't make sense (at first).