She shared the news with a photograph of the parents-to-be and a framed sonogram next to a white baby bodysuit labelled "Coming Soon".
Jewel's partner in season five of the Channel 9 "social experiment", Dean Wells, was among the first to send his best wishes.
"Woohoo!! So happy for you guys!!" he commented on the post.
Fellow former MAFS contestant Aleks Markovic said: "Congrats beautiful."
"Congrats gorgeous!" former Bachelorette Ali Oetjen added.
Jewel had her daughter with ex-husband Jacob Anthonisz.
She went public with her relationship to cast mate Sean Thomsen during the MAFS reunion episode in 2018 before they split after six months.
She rekindled her love with her Year 11 boyfriend Nathan after he messaged her in November of that year to get a coffee, she told WHO Magazine.
"He ended up taking me to a Wildcats [basketball] game, and that was it!" she said.
In May, Jewel shared photos of herself with Grace and her adopted mother on Mother's Day, admitting the celebration was a "mixed bag of emotions".
"Mother's Day can be more than honouring the person who went into labour and gave birth to you, but honouring the person who has been there for you through thick and thin, has offered you unconditional love and made you the person who you are today," she wrote.