When should I worry about reoccurring bloody nose? Sister has been getting them once a day for two weeks with headaches

See ENT now. You should see an ENT doctor immediately. Daily bloody nose with headaches is not normal and needs a work up. Please do not ignore this.
Now. She needs to be seen by her primary care doctor and have her BP checked and baseline labs, such as creatinine, sodium, potassium, thyroid. Also see an ENT doctor to evaluate the nose for bleeding lesions. Big concern is high blood pressure leading to increased pressure in the nasal passages causing bleeding. Hope this helps.
After treatment. Nosebleeds occur for a variety of reasons. In children, 90% of nose bleeds occur in the front near the nostrils, which is why pinching the nose helps stop it, since pressure is applied. In adults, it can also be posteriorly, so pinching helps in fewer cases. Use saline spray and aqueous nasal gel to see if helps. May need blood work and scope by ENT to look for nasal mass if does not get better.