Nymphomania in bitches

As some of you know....our Teegan is a slapper.
Last season she let Alfie mate with her on day 5-6....so I was taking no chances this time and sent Alfie on his Jollies to mums on day 3.
Brought him back last night and by my reconing shes day 19 possibly 20.He wasn't back 2 mins and I mean 2 mins and she let him jump her again......I'm tearing my hair out with this bitch...she's such a tart...I'm sure she's a nympho.....I know it is possible to get bitches with a high libido but have any of you had one like this.....What do you think.....I'm assuming she won't get pregnant but don't know whether to get her the morning after pill just incase.