While I see the frustration fighting with dark might, it can be seen as a skill to not pick a bad variant for the fight to begin with. Nevertheless, even he can win this fight if you keep up the pressure and time the grab bb2 correctly as it goes through stun and hits sufficiently often to not allow the MnF above 10% during the animation. This is probably the hardest method to kill a MnF with 5 perma regen so I would strongly advice against it, and just pick a variant that easily deals with her. Beast king, wulfsbane or weekend warrior if you want to use a beowulf for example.
Also, dont forget she doesn't just spawn in with 5 regen as it has conditions you can circumvent if played skillfully.
having a higher fighter score doesnt automatically translate to winning the fight =)