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The 19-year-old and 20-year-old sisters shared photos of themselves with their actress mother and wished her a happy birthday in the captions.
Loughlin, who pleaded not guilty to charges of conspiracy to commit mail fraud, among others in April, turned 55 on Sunday.
"One day late. happy birthday. i love you so much," Olivia wrote.
"Happy birthday mama. I love you," added Isabella.
Court documents unsealed on March 13 revealed that Loughlin and and her husband, fashion designer Mossimo Giannulli, "agreed to pay bribes totaling $500,000 in exchange for having their two daughters designated as recruits to the USC crew team -- despite the fact that they did not participate in crew -- thereby facilitating their admission to USC."
Emails from Loughlin and a recorded conversation between her and her husband, which were obtained by federal agents, implicated them in the scandal, dubbed "Operation Varsity Blues," according to documents.
The couple was indicted on a federal charge of conspiracy to commit mail fraud and honest services mail fraud, a crime that could get them each a maximum 20-year prison sentence if convicted. They were later hit with additional charges, including a count of conspiracy to commit money laundering, according to federal officials. They have pleaded not guilty.