I don't personally use them since our girl is spayed, but these ones have the top reviews on Amazon.

https://www.amazon.com/Paw-Inspired-Protection-Disposable-Diapers/dp/B073NY1LBB/ref=sr\_1\_5?crid=3OL9AW0648MCE&keywords=female+dog+diapers+for+heat+cycle&qid=1662389978&sprefix=femal%2Caps%2C123&sr=8-5