Okay, bit of a cliched topic here, I admit, but I'd like to throw some ideas out there, and I'd like to hear what you all have to say about it.
While it's pretty much established that Rubedo far outclasses Ainz in terms of stats and raw power, I think it would make a very interesting, and not on-sided match up considering the following:
Touch Me is probably one tier below Rubedo, and Ainz is maybe one and a half tier below Touch Me. However, Ainz (bit of a tryhard player) has access to cash items, the Staff of Ainz Ooal Gown and full Divine set (discounting World Items), which probably puts him on the same playing field as the likes of Ulbert and Touch Me.
Ainz has access to all NPC information. Rubedo's stats, moves, personality, tendencies are all available to Ainz. Ainz could easily build a strategy to fight her just like he did with Shalltear.
Ainz beat Shalltear. While Shalltear is presumably much weaker than Rubedo, she has the advantage of possessing a second life due to Peroroncino's favoritism and just so happens to completely counter Ainz's summoning build. The fact that Ainz won without his full equipment set, albeit with cash items, implies that he would probably be able to handle any floor guardian that didn't counter him with ease.
The above facts make me think that given prep time, a fully equipped Ainz could take on Rubedo and maybe come out on top? I know we don't know much about that enigmatic character but let's have a discussion just for the sake of it.
PS: Let's assume he doesn't use any world item or deploy the other 8th floor trump cards.