Christmas her 5th year, after Arthur Weasley had been attacked by Nagini, Sirius privately gave her an important present- his portkey to the unplotted island in the Pacific that the Black family owned. He told her he worried Harry wouldn't use it or would lose it, so he gave it to her for safekeeping. Looking back she could see the selfish manipulation. Sirius wanted Harry safe, her safety would be an ancillary benefit. He knew she would save Harry when he wouldn't save himself, even if it put her in danger. Well, her days of sacrificing for others were over. Once she had everything she wanted from Britain she was gone. She could live out the rest of her life in solitary safety while the world around her burned. In the future, she could reassess the situation and consider returning, maybe not to Great Britain, but elsewhere. Plus, she could offer Luna and Neville an escape as well.