One thing I would suggest you do in the event that your aunt doesn't pay you back as promised. Since you have decided that you will not let it harm your relationship, you should pick a timeline (in your own mind, not something to tell her!) where you inform her that you no longer expect to be paid back.
Sometimes, especialy in family situtations, despite all the good intentions on your part, even if YOU would understand not being paid back, the person who "owes" you becomes embrassed that they haven't paid you back and unconsciously will start avoiding you, or over-thinking anything that comes up and attibuting a disagreement to YOUR wanting the money, etc etc.
Cloak it anyway you like to allow her to save face... great time for a little white lie. "I had a great year at work and they gave me a bonus large enough to cover my cost of the cruise, so its not fair for you to have to pay. Let's go to dinner to celebrate!"