Hiya!
I had the idea that instead of going through every in heat lionesses in your dens, which could become annoying if you have a large number of them, and especially so if you have to do it every day, you could just hover your mouse over (or tap on for mobile users) the flame icon next to their name on the den page and it will show you how many days are left before she goes out of heat.

Please let me know if you have any questions or further suggestions about this, and please if you don't support the idea, tell me why in the comments