The fact her didn't kill her and made sure others didn't is respect enough.
It's possible to look down on someone but still be appreciative of their help
Did Broken Tusk view her as an inferior who helped him and who therefore deserved protection...or did he view her as an equal warrior? Was he giving her the mark simply to protect her from investigating predators...or did he actually think her worthy of membership in a predator clan? You can't tell from the comic. There's room for different nuanced interpretations
In the novelisation, Broken Tusk almost admires Machiko