Who said she becomes najis?
Najasat is only at the private parts. The rest of the body is clean.
As for the blood she sees, it's period depends on the bleeding. If the bleeding stopped for less than 10 days, then, it is all lying in (Nafass), while if it exceeded 10 days, then, she counts her period days as nafass, and the rest is Istehadha, . Hence, she performs Nafass ghusl, and starts praying.