I think it's close or maybe even inconclusive, but if I had to pick one, my vote goes to Libra.
I also want to add something to info above.
For Libra
1) People seem to forget that Brachius is AoE. I don't know what to judge about Limbo clones (as in I don't know if we're supposed to consider them to one-sidedly be able to attack her or if she can retaliate somehow) but if she can, it doesn't matter if there's only 1 or 100 enemies, she can brachium all of them at once. Meaning if she can hit them, they're all dead.
2) Assuming it's unhitable, Libra is stated to be able to learn from everything used against her as well as predict how her enemies will move/attack/do. So if Madara can't 1hko her, he won't be able to use the same strategy once. Even assuming Limbo clones do attack her without her being aware, if they can't 1hko her, she'll be able to predict what they will do after the first (or second time).
3) Novel states that Brachium disallows Alnasl (which teleports from one point to another in the same world/dimension). Meaning Madara won't be able to poof from one place to another if it's in the same world.
4) Similarly, novel explicitly states that Brachium can't be escaped by any means possible. So I assume this includes Dina's X-Gate. Dina's X-Gate allows her to travel between dimensions/world/space, meaning Madara won't be able to escape to another dimension using his skills. (I don't remember this part clearly, but I seem to recall earlier chapter saying something about Brachium being something to do OP things because it's related to the Goddess, hence why it has OP effects or w/e. Either way, my original argument is the same). This means that Madara won't be able to teleport away regardless of same or different dimension.
5) Even aside from Brachium, Libra has whole bunch of arsenal. Like for example, Astraea (we currently have it listed as, small planet level which is low 5-B? Unless we can't use Astraea?). And as far as we are aware, she can spam attack with Astraea. So it's bound to hit sooner or later. So I question if Madara can survive even if he can survive the initial Brachium shot with Izanagi.
So for those reasons I'm going to vote for Libra (even though I think that if these 2 fight 100 times, Madara will win a few times. That's assuming they start afresh and isn't 100 rematches with memory of previous fight, because Libra do the calculation thing then.). On a separate note, I read in the spoiler somewhere that she can spam Brachium later in the series. I don't know if that's true but if it is, it'll be an unfair matchup.