I'm not sure whether you could call it a "bloodline limit". We do know that her grandfather had herculean strength as well, so its possible that she inherited his immense strength. For it to be called a bloodline limit I guess would mean that they have an entire clan of super-human strength ppl - which for we all know does not exist. Why doesn't her brother have this strength? Well its possible that not everyone related to the 1st will inherit it.

Then again she could be "all-natural" and have inherited it through training with her family.
...Thats all that I think we can speculate about right now