Let me clear up the air here as someone who has finished Nier Automata twice.
One, 2Bs immortality means nothing, it will simply restart the fight all over again with her getting a different body, it doesn't mean anything.
Two, first sentence of OP, "speed Equalized if necessary" so it is Equalized here.
Three, her resurrection only has a 50% chance and a KO will work, though Nakagami armor will help.
Fourthly, "Try to analyze Erza would be too hard for her Armor change" Right, because Erza is going to have an easy time analyzing 2B, with her lasers, bullets, multi grenade launchers, both of her time manipulation abilities, one of which she won't know about, and the other can be shot at a distance. I haven't even talked about Gravity manipulation.
Erza has, better expierience, skill, and is much stronger up close, she can one shot 2B, while 2B is going to have a hard time getting past her armor without using time manipulation.
2B has a FAR greater variety of long range weapons, gravity manipulation to keep Erza in place and thrown Time manipulation can both keep Erza in place while 2B bombards her with everything I mentioned.
So 2B takes the range fight by a good margin margin, gravity manipulation can hold Erza in place, though Erza could probably switch to defensive armor to minamilize damage, and thrown Time manipulation will both hold Erza in place, and Erza will move and act much slower allowing 2B to get hits in while Erza is changing armors.
Now up close is an advantage for Erza by a slight margin, one hit will take out 2B once she finds an opening while 2B will struggle getting past her armor, but if 2B dodges that attack and activates time slow, she has a decent chance at taking an opening, and decapitating of stabbing Erza.
Therefore I give it to 2B with Mid High difficulty.