Of course you only refund "come " ticket when she returns from her holiday, give her the "leave" ticket when the 2 year contract ends. Don't pay for a 2-way ticket now, as she may never come back.
She is entitled to 7 days, but the exact time is subject to mutual agreement. Even for office workers, your boss need to approve your holiday! She can only leave subject to your convenience. You pick the time you are free to take care of your family. She cannot pick any day she wants. If it is inconvenient for you, you can refuse can give 14 days to her or cash in lieu when the contract ends.
If you can agree on which 7 days to let her take, you do NOT have to pay for the air ticket to and back as those are her holiday. DON'T advance any salary. If she can be so demanding, you have to stand your ground. Otherwise, 以後食住你.
My maid asked for a holiday even before 1 year is up due to a promise to his son who got in a top secondary school. Now, she wants another holiday in the same year as her husband is sick. I say no of course. Once you open the door, they will keep asking and asking for more holidays.