It doesn't look like brindling to me, looks like fur grown from neck creases.
But if you really think it's brindling, you can find out for sure by having her double DNA typed. Since brindle is generally associated with chimerism, Have a test done on several places on her skin, (including non matching color spots) and also on her blood. If the DNA profiles don't match, it means she's brindle. And it means she's also chimeric.