Yes, although ápolónő is also a word for nurse, if you want a less ambiguous one.
I would definitely say that "sister" is the primary meaning of the word nővér and you would only interpret it as "nurse" when the context strongly suggests it (like mentioning a hospital in this sentence). It's pretty similar to how "sister" can mean "nun" in English - but you wouldn't assume that meaning unless context strongly suggests it.
You are right. I reported the error. When you find a mistake check the box that there is an error. If you do a screen shot of your completed answer you can attach it to a bug report.