Maryam's mother Kulsoom Nawaz is on a ventilator after suffering a cardiac arrest in London where she is undergoing treatment for throat cancer.
"We found her unconscious and when I was returning back home, she opened her eyes and saw us but could not talk," Maryam was quoted as saying by the Express Tribune.
"I wish to hug her in healthy condition," she said.
"They want to make me a weakness of my father (Nawaz Sharif) but luckily, now I am a source of strength," she said in the audio message.
She asked her voters to prepare for the July 25 general elections.
"If I was not in prison, I would fight this historical democratic battle with you on the streets," she said.
Maryam said that she was contesting election from a single constituency but now she is contesting for all the 272 constituencies.
Both Sharif and Maryam have been sentenced by an accountability court to 10 and 7 years in prison respectively.
Sharif was disqualified by the Supreme Court last year in the Panama Papers case.
Sharif has been one of the country's leading politicians for most of the past 30 years. He remains popular, especially in Punjab, the most populous and electorally significant province.