Brazilian Butt Lift Using my Sister's Fat?

The only person who could be used for a fat transfer is theoretically an identical twin sibling. Otherwise donor fat is not acceptable.

Hi there-
The Brazilian Butt Lift is a fantastic technique that we do often with great success-- but could not be done using your sister's fat (unless she is your identical twin).
This is because your body would re-absorb the fat almost immediately after injection, recognizing it to be from another person.
In patients like yourself, often the best strategy is to have you gain a bit of weight. Once you have enough fat to redistribute to your particular goal, the procedure can be done. After the surgery you can then lose the additional weight, with preservation of your new shape- in other words you will lose weight everywhere, but the shape and proportions achieved at surgery would be maintained.