Translation:My aunt is going to the US on Saturday evening.
The literal meaning of 阿姨 is an aunt who is your mother's younger sister. When I was in Beijing, I heard this word commonly used to refer to a woman who watches children (a nanny). I suppose your experience shows that it is used more broadly than that. Chinese culture has a huge family focus, and it is more common in Chinese than English to use family words to refer to people who are not actual family members. For example, my Chinese host once addressed an old man passing by as "Grandpa" (姥爷) to ask for directions. If you watch the Ip Man movie, you will see that Ip Man's friend addresses Ip Man's wife as "sister-in-law" (implying that Ip Man is his "brother".) I hope that gives you a sense of how family words are sometimes used.
Yes. Not to mention that it was seemingly designed more with phonetic scripts in mind as in European languages etc., where any alternate pronunciations of characters always have the context of a word around them, even in the word bank, that ensures the correct pronunciation.
Annoying enough here when the wrong pronunciation of a character is used from time to time, but over in Japanese the word bank pronunciations are a hot mess.