Okay. I believe that this is going to be a bad match-up for tsubaki. Well big deal since most hers are anyways. I believe it is around 6-4 or 6.5-3.5 Mu's favor. This is because of her laser/cross-up pressure and a lack of a good way to get around it.
Example Time!
This is the most effective strategy of Mu that I have seen so far. When the Mu player had the stein positioned around the ragna, it was very easy to set up for the cross-up. Now rhe ragna could have dp'ed out of that situation, but that is the problem. Tsubaki doesn't have a good dp. The only move that I can think of that would help is 236D, but that costs charge and getting charge is going to be hard in this match-up because if Mu gets her steins set up, it is bad news for Tsubaki. This means that Mu players are going to be watching for it. Though that can work both ways though via mind games. It might make the setup not look so good if the tsubaki player has a charge saved.
The only way I see this going well is if the tsubaki player does rushdown like no other and goes for the oki on ground combos. I can maybe see charging for up to one charge after an air combo finish, so you can get charge but still have time to keep some pressure up on Mu, but that is entirely speculation.
I might suggest trying to throw in the unsafe charge blockstrings to try and get that 1 charge, but hey it is risky. We should also watch out for Mu's chargeup attack since it can break 3 guard primers. Going on the defense is a big no-no since Mu has the potential be the best guard breaker in the game.
So the short story is, be super agressive and don't let Mu set up her steins and tsubaki has a chance of winning.