User blog comment:B214/Volume 21 info & spoilers/@comment-104.7.80.211-20160523010126/@comment-73.160.58.215-20160523022602

I don't think she actually can wield Incinerate Anthem. Even within that chapter, it was pointed out how that Longinus "chooses" its next wielder. When Walburga was defeated, it abandoned her but was captured by the DxD Team and handed over to their superiors in order to avoid it falling into the hands of another enemy. The cross Valerie has seems to be simply a "vessel" to hold the ownerless Longinus (adjusted in order to keep it from harming her) and allow her to make use of the resonance with Sephiroth Graal for the sake of rendering the enemy's Holy Grail powerless. Thus, you can't say that she truly possesses both Longinuses.