Wait, I just realized something. I'm not sure if I'm overthinking things (i.e. feel free to disagree/add on), but it felt like Fang kinda tried to commit suicide after her babies were eaten by Big Red.
The reason I say this is because she runs not at Big Red, but around at first with her eyes closed, like she's grief-crazed (which she is, justifiably so). And it seems to confuse Big Red (and the viewers), until she basically runs right under Big Red's foot without even trying to attack. Fang doesn't even open her eyes or struggle at all as Big Red is about to kill her, and she only opens her eyes when Spear jumps on her back to save her.
I feel this parallels Spear almost committing suicide and then having a vision of his family and deciding not to. Fang pretty much does the same and then decides not to when she sees Spear risk his life to save her. She's hesitant a bit and confused, but then she's 100% on board.
Again I might be reading too much into this, but I feel Fang (and to a lesser extent Spear) decide not to commit suicide because while their families have been killed, they can still find new ones (i.e. each other) and live on.