Situational differences between 姉、姉さんand お姉さん

Could someone please confirm, add or correct the following situational uses for 姉、姉さん、お姉さん:
1. 姉（ane)-Used when speaking directly to one's own older sister or formally about one's sister to others.
2. 姉さん（neesan)- Used when speaking directly to one's own sister, informally about another person's sister or in a familiar way to a girl older than you with unknown name.
3. お姉さん(oneesan)- Used when speaking formally about another person's sister or in a familiar way to a girl older than you with unknown name.
Dictionaries list all three with the same meaning (older sister) but they don't list how they differ in situational use. Is there a useful resource for checking the formality level of Japanese words/phrases or is it just trial and error?

Your best bet is to read things and watch shows/movies/actual people talking, and you'll see the appropriate uses bubble up from the context. If you're speaking to Japanese people, you can always take a stab at it, and ask them if you used the right word

Thank you.

You'll find useful explanations if you learn from a textbook instead of just looking things up in a dictionary. Some things are too complicated to fit into the limited space of a dictionary entry.