Plausible way to redeem Madoka...? Unfortunately, we don't know enough about why she wants to ax Chifuyu to make any legitimate guess.
Only way to redeem her is to have something ELSE become so big a threat that it would essentially force Madoka to side with the good guys for a turn. That or somehow get rid of her obsession with killing/maiming Ichika...
not an easy thing to do right now.