Baby Sully bounced between the NICU and CICU until she was about 5 weeks old, when doctors determined it was time for her to undergo open-heart surgery

Baby Sully. PHOTO: COLLEEN WEIMER

A New Jersey family has a lot to be thankful for this Thanksgiving now that baby Sully is finally home.

“It was just the best feeling just to finally be in our house, under one roof,” mom Colleen Weimer tells PEOPLE, sharing that having the “amazing” 7-month-old baby home following a series of health complications is remarkable.

Born following a tough pregnancy, little “Sully Bear” underwent major heart surgery for a rare cardiac birth defect and spent 158 days in the NICU at Children’s Hospital of Philadelphia. She finally made it home in September.

From the beginning, Weimer, 37, said she knew there was a “possibility” that she could have preeclampsia — a serious blood pressure condition during pregnancy, per the Cleveland Clinic — which she experienced while pregnant with 7-year-old daughter Quinn, who was born at 28 weeks.

“I was worried about the possibility of having a premature baby,” she says. “Then, when we went for our 20-week scan, we found out that things were a little bit more serious.”

The mom says doctors saw something that “didn’t look right with the baby’s heart.” Although they didn’t seem “totally alarmed,” they wanted her to undergo a fetal echocardiogram.

“So we went somewhere locally and did that and when they did that, [another doctor] still felt like things didn’t look totally normal,” she adds. “She thought she saw something called transposition of the great arteries, which is when your aorta and your pulmonary artery are switched so your blood can’t oxygenate.”

That’s when she and her husband were recommended to go to CHOP. And when she was around 22 weeks pregnant, Dr. Elizabeth Goldmuntz, an attending cardiologist in the Cardiac Center at CHOP, confirmed Sully had a congenital heart defect and would need open heart surgery after she was born.

Weimer says that Goldmuntz “seemed pretty concerned about the idea” that she “could possibly give birth prematurely,” noting that “when you have a baby with a heart condition” a premature birth can be difficult “because the heart’s so small to begin with, and those vessels and everything need to be developed.”

“We were just hopeful that we could get the pregnancy as far as we could,” she says.

And on April 17, Weimer — who happened to be celebrating her own birthday — gave birth to little Sully at 30 weeks. “She’s my birthday twin,” she say of the baby, who weighed only 2 lbs. 3 oz.

Baby Sully.COLLEEN WEIMER

Still, after her little Sully Bear was born, Weimer tells PEOPLE that doctors were worried she wouldn’t survive.

“She was so tiny at that point that they didn’t know she would make it through an open-heart surgery,” says the mom.

Baby Sully.COLLEEN WEIMER

Initially, Sully was placed into the Cardiac Intensive Care Unit at CHOP, where Weimer says they weren’t “used to having a baby that small.” After about a week, Sully was “doing great,” but the mom says doctors “felt like she needed to grow.”

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Sully ultimately bounced between the NICU and CICU until she was about 5 weeks old, when doctors finally determined it was time for her to undergo an open-heart surgical procedure called the Arterial Switch operation to reconstruct her heart.

Baby Sully.COLLEEN WEIMER

The hospital says the procedure has been performed since the 1960s, but it was rare to perform on babies as small as Sully, who only weighed about 3.5 lbs on surgery day.

Reflecting on that scary time, Weimer says she is deeply thankful for her “really supportive family,” like her parents and mother-in-law who took care of Quinn and 9-year-old Reid as the family lived about two hours away from the hospital.

“With her being so unstable, I didn’t ever really feel comfortable going home,” the mom adds.

Baby Sully.COLLEEN WEIMER

Following 158 days at CHOP, Sully was finally healthy enough to head home — and she’s already made a big impact on the family.

“After everything that she’s been through, it’s just absolutely amazing that she could come through it and just have the sweetest little personality, and we just absolutely adore her,” Weimer says.