In this regard you'll have to dodge her attacks, don't try to jump out, and backdash when you get the chance, I understand how her 6C works, but if she whiffs an attack due to your backdashing, she won't have the time to actually hit you with it, you'll block it at worst, if I recall correctly, her DP is super unsafe on block, so I don't quite understand how it's unpunishable for you, learn to IB it, that way it's more beneficial, because you get even less recovery IBing something in the air than you do on the ground. Her steins aren't doing anything if she's not setting them, and they are easy to dodge, due to Arakune's air mobility, he can avoid lasers and Mu at the same time if you know what you're doing. From what I've seen Mu's mixup is worse than Ragna's, if you spend a little time to learn how to block, then her melee game isn't all that good as far as pressure goes.
Still, the match up revolves around being patient and biding your time, the stage is neutral if the lasers can't hit you, and Arakune has more tools than anyone else to make sure they don't.