I personally prefer Ur-ma. Ur-ma sounds like the former name of Myanmar (Burma) and I always liked saying Burma because it rolled off the tongue so well, same thing with Ur-ma. As for Eer-ma, I don't know. I feel like Eer-ma doesn't suit "Irma" and should be spelt as "Erma" but then again you wouldn't pronounce "Ermintrude" as "Eer-min-chrood", would you? You could spell Eer-ma as Earma but you wouldn't pronounce "Earnestine" as "Eer-nes-teen", would you? Plus the Ear part would cause teasing. Tl;dr: I prefer Ur-ma over Eer-ma as the pronunciation for Irma.
Tl;dr: I prefer Ur-ma over Eer-ma as the pronunciation for Irma.