why is another option not she opens the bottle?
It should be.
Because Ανοίγει can be used for both genders, unless it specifically puts 'He/She' before the verb.
It is an option. Did you use it and have it rejected? Please let us know because it's been in the incubator since the start.
Opening the bottle was marked wrong??
Yes. "Opening the bottle." is not a complete sentence because in English, unlike in Greek, you can't leave out the subject like that.
You have to say "He is opening the bottle.", for example.
Thanks for the answer you are right it's not a complete sentence but Duolingo has hundreds of incomplete sentences which are marked right
True; if the original is not a complete sentence, the translation will generally be an incomplete sentence as well.
But in this case, the original Greek is a complete sentence.
Το μπουκάλι πορτοκάλι δεν είναι ασπρόμαυρη.