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Decimation
If she wasn't Azula's oldest friend; she would have hated her. As it was, if she didn't obey unquestioningly, her clan was forfeit.
Uncles, cousins, wedded aunts. Any one clansmen in ten could be executed at any time for any infraction against her princess. It made more sense that she put herself forward instead and at least increase the chances that the household would survive strong into the next generation.
The moment that Zuko took the throne, she had that despicable practice outlawed for even the Firelord.