Then, about two months ago, the 2-year-old's parents got a devastating diagnosis - Zainab has neuroblastoma, a rare cancer that mainly affects children.
Zainab Mughal has neuroblastoma and needs life-saving transfusions. Narrowing the field further is the fact that donors would also need to be missing the "Indian B" antigen commonly found in blood, just like Zainab.
Donors need to be exclusively of Pakistani, Indian or Iranian descent, meaning both parents must be 100 percent of one of these ethnicities. But OneBlood says Zainab is going to need a lot more blood than three donors can provide to beat the cancer.
Donors must reach out to OneBlood in advance to ensure the additional compatibility testing is performed. Because the antigen is so common, it makes it hard to find blood donors who are lacking it as well, Forbes said.
Her parents' blood is not compatible, said the child's father Raheel Mughal. "This was the worst thing we were expecting".
Around 800 children in the USA are diagnosed each year with the disease and most are diagnosed when they are younger than five. Three matching donors have been located, including a donor from the United Kingdom.
According to St Jude Children's Research Hospital, neuroblastoma accounts for seven to 10 percent of childhood cancers.
"This is all hands on deck", Frieda Bright, OneBlood's reference laboratory manager, said in a video promoting the search.
The cancer can spread to tissues beyond the original site, including bone marrow, bone, lymph nodes, liver and skin. According to the American Cancer Society, there are about 800 new cases of neuroblastoma diagnosed each year.
As the search continues, the little girl's family is already expressing gratitude to all the people who have shown up with a desire to help Zainab in her battle with cancer. And more than 1,000 people who are of Iranian, Indian or Pakistani descent have donated blood to be tested, Forbes said.
"My daughter's life very much depends on the blood", Mughal said, describing the plea for help as a "humble request" from his heart.