She never regreted it. she was glad she killed him because he almost gave away the fact that Hollyleaf, Lionblaze and Jayfeather are not Squirrelflight's kits.
In the book "The Forgotten Warrior" from the Warriors series by Erin Hunter, Ashfur's last words were "You'll regret this. You'll all regret this. I promise you that." He says this before he is murdered by Hollyleaf.
Ashfur's murderer is Hollyleaf. Leafpool found a tuft of Hollyleaf's fur snagged in Ashfur's claws.
Hollyleaf
No, Hollyleaf did.
Hollyleaf
no one
Hollyleaf was the cat who killed Ashfur. She did so to protect her siblings and keep their secret from being exposed.
No, Hollyleaf does. It may seem like Squirrelflight did but she didn't 'cause Hollyleaf admits that she did kill Ashfur in Sunrise.
Ashfur-Revenge
Hollyleaf hollyleaf[for certain-positive-sure]
It depends on what you think evil is. Hollyleaf does kill Ashfur though.
No, Ashfur would never try to kill Squirrelfight. He loved her but tried to kill Hollyleaf, jayfeather, and Lionblaze to get revenge on her. Then she revealed they were not her children and he didn't kill them.