Rutgers graduation: How grieving mom found a new mission in life (WATCH)

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Deborah Horenstein began her professional career in finance, a Columbia University graduate who'd studied economics. She built a life — with a husband and three children, and eventually a home in Fair Lawn, N.J.

But life was difficult for Horenstein's youngest daughter, Ariella, almost from the beginning. First it was a blood problem at 4 months old — idiopathic thrombocytopenic purpura, a disorder that can lead to excessive bruising and bleeding. Crohn's disease at 2 years old. Epilepsy at 4. Through that all, Ariella struggled with an immune disorder not quite like any her doctors had seen.

"That didn't stop her from being the happy person that she was," Horenstein told New Jersey 101.5 from her current home in Monsey, N.Y. "People were always amazed that even though she had so much pain from a lot of different parts of her complicated illness, she still had such an amazing spirit.

Join New Jersey 101.5's Bill Spadea and Mike Symons of New: Jersey Decoded for a live chat as New Jersey 101.5 streams live video of President Obama at the Rutgers Commencement Sunday. The ceremony begins at 12:30 p.m.

"It really encouraged people to try to find the good in their life. ... And she never complained, she never complained. It was really remarkable. It was really such a lesson for people. Because if she didn't complain, then what did we have to complain about?"

In 2007, at age 8, Ariella seemingly unstoppable laughter fell silent. She died of complications from a bone marrow transplant a year and a half earlier — one that had her family relocate to North Carolina for treatment at Duke University Hospital.

Throughout Ariella's treatment, Horenstein became an unofficial medical expert, setting up something of a mini-ICU in her North Carolina apartment. Ariella saw several specialists — but it was her family who knew how all the pieces fit, who knew her history, who knew her treatments intimately.

Horenstein had considered during that time entering the medical field — but knew that even if her daughter survived, she'd require continued, extensive care. When Ariella passed, Horenstein eventually had the time to engage in more in-depth studies.

"Because (Ariella) was so complicated, I thought about how I could use it," she said. "What can I do to help other sick children? Because I have a strong faith, I felt like I was given this complicated child for a purpose. I decided that purpose was, or I felt like that purpose was, to help other sick children and their families.

"Because I had been on the receiving end of medical care, and I knew what kind of impact a really special physician can have on a family with an ill child."

This weekend, she'll graduate from New Jersey Medical School — beginning her career as a pediatrician.

Horenstein said she's grateful to NJMS for accommodating her particular needs as a devoutly religious Jew — and for making diversity among the school's community a priority. It's part of why she'll continue at NJMS for her pediatric residency. She's hoping for a pediatric neurology fellowship beyond that.

For more on the Horenstein family's efforts to help young children — including information on the Ariella Hornnstein Music in our Lives program to provide music-related activities for youth, and the Ariella Horenstein Bikur Cholim Society of Duke to comfort and support families grappling with illness at the hospital — see Horenstein.org.