There is some difference between ‘to Hawaii’ and ‘in Hawaii’.
The former suggests that Ms Taylor has left for Hawaii on vacation and the latter that she is currently visiting Hawaii on vacation. (Both are acceptable)
Yes, I would use the comma because the speaker is addressing her.
Vacation in Hawaii is probably slightly more common but both are used. We are supposed to use a comma before direct address like Ma’am. However, lots of punctuation tends to be left out in internet usage. We often use a kind of abbreviated and slang style in social media posts and texts.