A temple virgin uncovers a secret that the high priest would rather conceal: the Day of Atonement isn't working anymore. When he marries her off to a hundred year-old man, she loses everything she's ever known. Now she must find a way to prevent another unjust marriage — and restore the Atonement — before it's too late.

You have two inciting incidents in the logline.

She uncovers a secret
When she’s married off to a hundred year-old man

I would concentrate on the ‘day of atonement’ angle for the logline and keep the ‘forced marriage’ story for the script itself.
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“When a devout temple virgin discovers the ‘Day of Atonement’ isn’t working, she must battle against the power-hungry high priest who will stop at nothing to keep her knowledge a secret.”
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Hope that helped, good luck with this!