CAIRO — Confined to a tiny windowless cell without a mattress or a toilet, denied visitors and held in solitary for months on end, Ola al-Qaradawi is being subjected to harsh treatment even by the grim standards of Egyptian prisons.

Ms. Qaradawi, 55, was arrested in June when national security officers swooped in on her family’s summer villa on the Mediterranean coast. Since then, her lawyers say, she has been denied the most basic privileges, and is allowed a single, five-minute bathroom break every morning.

What crime merits such tough conditions is unclear. The Egyptian authorities have yet to formally charge Ms. Qaradawi, who works in an embassy and is a permanent American resident, or her husband, Hosam Khalaf, who is being held in similar conditions at a separate Cairo prison. State news media outlets say they are accused of belonging to the banned Muslim Brotherhood.

But the true reason for Ms. Qaradawi’s punishment, supporters and human rights activists say, is more likely tied to a bruising geopolitical feud between the biggest and wealthiest countries in the Middle East, in which Ms. Qaradawi may have become a hapless pawn.