"Žofie, you are a good friend."
Translation:Žofie, vy jste dobrá přítelkyně.
Milica, I agree with your teacher. If you're under 50 and in Prague and use the word "přítel/přítelkyně", it will be interpretted as "boyfriend/girlfriend", regardless of your or your friend's gender.
Outside of Prague and/or in older people's speech and/or in special circumstances where it's somehow clear that the speaker does not mean a romantic partner, "přítel/přítelkyně" may be used to mean a good, trusted, sincere friend. The word is old-fashioned, and it has a heavy tone today, it can't be used for a buddy or acquaintance. It even sounds a bit too serious when used for boyfriend/girlfriend, at least in Prague, and other expressions are preferred, based on individual taste.
I have asked my friends in a Czech forum the other day, how they perceive the word přítel when uttered about a přítel of a male person and they agreed that they do not understand him to be a gay partner. In these circles the word partner would be normally used. It may have changed in the recent years but in that case it won't be universal. (I and those people are currently 30-50).
For example: "Casanova ve svých Pamětech zaznamenává , že jeho přítel , hrabě Tiretta de Trevisa , v průběhu popravy čtyřikrát zezadu pomiloval dámu , za níž u okna stál" Not only it is very unlikely he was his gay boyfriend, I would even find the word kamarád to be completely inappropriate here.
That is not the full truth. Firstly, when they are of the same gender then (přítel/přítelkyně) normally mean just a friend. Secondly, even in English a girlfriend of a girl is just her female friend. Thirdly, when you say "jsou přátelé", "jsou přítelkyně", it always means "they are friends".
Olda and the singer are not gay partners, they are just friends https://www.youtube.com/watch?v=JayYApaMGsA
So I was informed by my Czech friend that kamarád and Kamarádka are more common for "friend" while přítel and přítelkyně are more common for boyfriend/girlfriend. I'm sure that it can have both meanings and I'm assuming that the word that is taught here on duolingo is more formal, correct?
Yes, your friend is right, although opinions on this matter vary. Generally, "přítel/přítelkyně" is very formal when used as "friend" and as such, it usually means "sincere, trusted friend". More often, it's used as "boyfriend/girlfriend", but a lot of people wouldn't even use it for that, preferring "můj kluk / moje holka" or "můj milý / moje milá" etc. "Kamarád/kamarádka" are the most common words for "friend". Then there's the colloquial-informal "kámoš/kámoška" which corresponds to "buddy" or "pal".
Please read the previous discussion here. It certainly needs to be a feminine word. Some will use only kamarádka, some would also allow přítelkyně, but it needs to be a feminine word. Přítel is a male person, be it a boyfriend or just a friend.
Of course in plural, přátelé, can be any friends, male or female.