With my persistent broody, I removed her from the nest and coop every single day for 3 weeks before she gave up. I will be investing in a wire cage the next time I don't want her broody.
You can try putting her in a broody breaker cage. A wire dog crate that has room for the hen, food and water works great for this (at least that's what I've read from some experienced chicken keepers here). Elevate the cage a bit so her belly can cool down, and leave her in there for a few days.