Ok ill admit Mei can't solo but if her and Haku works together they take this.
I think that Konan and Tenten Pull an extreme diff.
No one is Seeing Tenten in CQC, and it will be a constant battle on both Haku and Meis stamina, but won't hinder Konan due to the perfect aim. Haku will not be able to move faster in the mirror than Twin Dragon can hit, and explosive tag Kunai will render Silent Killing useless (smell and hear the explosion).
Konan is harder than steel as long as she has chakra manga fact, so none of Haku's attacks are phasing her. Her paper will decimate the senbon. Water does not affect her paper (she lived in Ame for Christ's sake) and she has unlimited paper, to use at any time. She is also more mobile than Mei, and should be able to avoid Lava. Boil is another story, but so is Mei's ability to dodge Explosive paper.
It "boils" down to whether or not you believe Tenten is a match for Haku, because Konan just barely edges Mei out, and if Haku can separate the battles she wins. If not, Mei and Tenten have abilities that mesh well together, so they mid diff. Separated, they still high diff 6/10