Female on heat

Can antbody offer any advice, as we have 4 cats, 2 female and 2 male. The latest arrivals came via my brother as he has moved and the cats cannot go with him, which is no problem. Anyway all the cats have been spayed, but the female has been on heat twice now, even though she has been done!!
Can anybody tell me why 1 female is perfectly happy and ok and the other one is a randy as a sailor in port!
Also is there anything that can be done to stop her!
Finally none of the cats go out as there is a lot of cat diseases where we live
Regards
ginger ninja

I've heard of this happening, but I've never heard of anything that can stop it. I'm surprised none of the males are trying to work their magic - When my cat was in heat, she was trying to go at it with my neutered male.. Recently, even though she's not in heat, and he's, you know, not equipped, they were trying anyway! Who knows. Maybe she's just, you know, lonely

Moving this to health forum.