Lowell shared several posts from the bash on Instagram, including a smiling photo of her younger daughter.
She and Baltierra are also parents to 9-year-old daughter Carly, whom they placed for adoption as teens.
"HAPPY BIRTHDAY to my beautiful, smart, independent, sassy girl!!!" Lowell captioned the picture of Novalee.
"Dad and I love you so much and love watching you grow!!! I just can't believe you are 4!!!!! #novaleereignbaltierra."
Lowell also posted snapshots of the unicorn-themed decorations and desserts, as well as a video of her guests singing "Happy Birthday" to Novalee.
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"My heart #novaleereign," she wrote.
Baltierra had shared a family photo with Lowell and Novalee on his account Monday on New Year's Eve.
He hinted at his recent marriage troubles with Lowell in the caption.
"Can't believe our little baby is going to be 4 tomorrow!!! As I look back on this past year, I'm reminded how blessed I am regardless of all the hard times we have experienced," the star wrote.
"I love my family more than words could express & I'm so happy where we are in life & proud of all the work we have done & I just love the love we all share in this little family tribe we created & I can't wait to meet the newest little member! #HappyNewYear #HappyBirthdayNovalee," he added.
Lowell and Baltierra announced in October they are expecting another baby girl.
Baltierra spoke out in December after spending 30 days apart from Lowell amid her pregnancy.
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