Lambda beats us in this matchup no question, imo. Her zoning is better than ours, but our mid-range game trashes hers. The problem is getting close to her. Mu does indeed have to kind of rush down in this matchup, putting her out of her comfort zone. You have to be VERY patient against Lambda. You're gonna be moving forward a lot and blocking, trying to get to the range where it's unsafe for her to do things. Once you have pressure on her you can keep doing it. She's got no options out without meter, and Calamity sword is so very baitable.
Mu has to take a lot of risks to close in on her. Mu usually forces others to take risks to get on on her not the other way around, so you really need to change your entire game plan for this one. That makes it pretty difficult. Lambda's zoning does have holes in it, so you have to find them and act quick on them. Otherwise you'll just lose.
My guess is 6/4 lambda but in Mu's favor once she catches her.