According to an interview with TV Tokyo, the IHA did not include Princess Aiko's tiara fee in the FY2021 budget "in view of the coronavirus pandemic." Usually the IHA budgets about 30 million yen for a princess' coming-of-age tiara/parure from the public funds it manages. Princess Aiko's tiara will either be paid from the Imperial family’s daily expenses fund or she will use a tiara previously worn by another princess.
I think she'll get a new tiara. Her aunt (ex-Princess Nori) Sayako Kuroda's tiara was also paid from the daily expenses fund. Sayako turned 20 in 1989 but her coming-of-age events were delayed for a year due to Emperor Showa's death and mourning period. The FY1989-1990 IHA budget was already huge for the funeral, tomb, and Emperor Akihito's enthronement. I saw some grumbling on Japan twitter that Princess Mako's tiara/parure was still paid from the IHA public fund despite the 2011 disaster.