The ruby has two completely different origins.
1) she stole it in Cairo as a child, and it's Candra's[the External] 'heart'(like a horcrux).
2) it's a family heirloom from her mother N'Dare, whose family has protected it for millennia; it is part of the 'Madripoor set' that can open transdimensional portals
Incidentally M'Rinn also gave her a transdimensional portal opening crystal in one of the classic X-Men backup stories.