"The only thing different about that day was that shot:" Did a trip to the doctor kill a healthy 12-year-old girl?

WAUKESHA (WITI) -- A disturbing mystery -- and a tragic end to a very young life. A 12-year-old Waukesha girl is dead -- and there is seemingly no reason why -- except perhaps, one.

Meredith Prohaska was an active, fun-loving 12-year-old girl one minute. A few hours later -- she was unresponsive on the floor. In between that time, there was a trip to the doctor -- and now, Prohaska's family wonders if that's what killed her.

"I'm a tough guy. I can take a beating -- but this has ripped a hole in my heart," Prohaska's father, Mark Prohaska said.

Prohaska is describes as a girl who loved to be active -- swimming and playing basketball while in sixth grade at Butler Middle School.

She loved to take part in activities at Horeb Springs Park.

"Vibrant. Full of life. She was our sunshine. Everywhere I go, everything I do -- I see her," Rebecca Prohaska said.

That's where a FOX6 News crew met her mother on Thursday, August 7th to talk about the young girl's unexpected death of July 30th.

Rebecca Prohaska took her daughter to the doctor for a sore throat. While they were there...

"She got her first HPV vaccine at around 10:30, 11 o'clock that morning," Rebecca Prohaska said.

At some point, Rebecca Prohaska says she remembers getting a handout about possible side effects.

"Thirty minutes later she was trying to sleep. I kept waking her up," Rebecca Prohaska said.

By 3:30 that afternoon, Rebecca Prohaska went out for a half-hour to get food.

"I came back and I found her on the floor," Rebecca Prohaska said.

Rebecca Prohaska -- a 14-year veteran EMT for the National Guard, performed CPR after calling 911.

Meredith Prohaska was pronounced dead at the hospital. No one could say why.

"It was the hardest thing when they called and said they don't know. There was no reason. She was the healthiest 12-year-old," Rebecca Prohaska said.

Rebecca Prohaska remembers a rare potential side effect of the HPV vaccine -- an allergic reaction, but Meredith's autopsy report rules her cause of death as inconclusive.

"The only thing different about that day was that shot. I wish I would've known more about it before I agreed to it," Rebecca Prohaska said.

"It has to be that vaccine," Mark Prohaska said.

The Prohaskas have donated Meredith's organs and tissue so others can live a healthier life.

While her family waits for more tests -- hoping for answers, they have a message for others. It's a message the family is spreading on Facebook, and on a GoFundMe page set up in the young girl's honor.

"Be aware of every possible side effect -- and make sure you're hugging them all the time because you never know when you're just going to be left with pictures," Rebecca Prohaska said.

Meredith Prohaska will be buried on Saturday, August 9th.

Meanwhile, Dr. Geoffrey Swain -- a professor and medical doctor at the Milwaukee Health Department says by and large, the HPV vaccine's benefits far outweigh the risks.

"Vaccines in general and the HPV vaccine in particular, very, very safe. It's a very safe vaccine and very effective," Dr. Swain said.

Dr. Swain says serious side effects are nearly one in a million.

"Very, very rare," Dr. Swain said.

CLICK HERE to learn more about the HPV vaccine via the Centers for Disease Control.