"Lena's strength inspires me to be stronger for her," her mother, Erin Tietjen, told ABC News. "Seeing her beat the odds on a daily basis gives us faith that she will be our miracle."
Lena loves being read to more than "almost anything," so her parents said they wanted to do something nice for her and came up with the idea of a book drive called Lena's Library.
"She loves to be read to," said her dad, Matt Tietjen. "She was always the one who would grab a book and take it to the corner to try and read it herself."
After Erin Tietjen's sister set up a GoFundMe page for the family mentioning Lena's passion for books, droves of deliveries started pouring in for the brave young girl.
"Saturday we got the first delivery, with about somewhere close to 150 boxes," Matt Tietjen said, adding that they have received hundreds more since then. "Some of these packages were full with more than one book. This one box alone had 17 books in it," he said, overwhelmed by the kindness of strangers who heard his daughter's story.
"People are so generous, and almost everyone sends a note to stay strong, 'We're here for you,'" he said about the gifts, which have included books not only for their daughter but also for their son and even for them. "I never knew so many people would send things."
The Tietjens found out at the end of October that their daughter, Evangeline, who goes by Lena, was sick after what they thought were typical stomach virus symptoms escalated to weakened motor function on her right side.
Lena was moved to the intensive care unit and received an MRI, and surgical teams performed a biopsy and surgery, called a ventriculostomy, the following day to help drain the excess fluid, her dad said, to determine the type of tumor and course of treatment.
Lena has an anaplastic astrocytoma, a malignant brain tumor, in a spot where an operation isn't possible.
"[Her doctors] initially said that without treatments, she would have three months to live," Matt Tietjen said, adding that they were cautious about the prognosis. "But they were hopeful that chemotherapy and radiation could extend that to one year."
Dr. Jane Minturn, the CHOP's director of clinical operations in neuro-oncology, who is working on Lena's case, told ABC News that Lena's grade III tumor is "very aggressive and invasive."
"Lena is a mature, precocious and articulate 4-year-old," Minturn said. "She has amazed every person who has treated her."
The Tietjens said they knew right away they had to fight and stay strong for their daughter and her twin brother, Clark. In addition to the treatment at the CHOP, they opened her case to other hospitals on the forefront of brain cancer research, including Johns Hopkins, the UCSF Medical Center, St. Jude's, Memorial Sloan Kettering and Dana-Farber.
"We will take Lena anywhere we need to in order to make sure that we fight for her," her dad said.
In the meantime, he said, she has been "extremely brave," and the whole family is thinking "in a brighter direction."
"The books are a tangible representation of the love, prayers and support for Lena's journey. Every time we look at them, we know we aren't alone in this fight," Erin Tietjen said.
She added that she and her husband have read to Lena and Clark daily since they were born and want to continue that as long as they can.
Matt Tietjen said Lena is generally "smiling and happy."
"She's just happy to be with her twin brother and having her cousins coming over to visit," he said. "She's in good spirits. She is trying to be her normal self."
"While so much has changed in our lives so quickly, the one thing that we can keep consistent for our children is snuggling together and reading a book," he continued. "No matter what physical limitations and challenges that Lena faces in the future, we will always be able to share this experience and sense of normalcy, even if it's just for a few minutes."