Same as with Foot and Mouth and other livestock diseases - to stop it potentially spreading. Whether this is the best policy is another argument of course - one you should take up with DEFRA, not me.
I've answered your incoherent comments as best as I can. Plus my argument has full weight of the law - your's doesn't !
There are few short-haired cows who can comfortably take a British winter. If you leave them out they suffer badly and lose many calves. Unless your daughter's herd was Angus or suchlike then she was opening herself to prosecution anyway.
Did she supplement their feed in winter using a feeding trough ? If she did the badgers will have walked in it, if she didn't she'd have starving cows.
I would gladly seek a prosecution of you if you did either now. They are a protected species and idiots like you harassing them deserve the full weight of the law on your backs.
No animal is as dirty as humans, except possibly rats. Badgers are vicious but only to escape.