There's a detailed report on the trial
here. It's more to do with whether either defendant could reasonably believe she had consented. The mens rea element of rape is intention to penetrate and that the defendant did not reasonably believe that the victim would consent. No mens rea, no crime... The jury is able to take into account all the circumstances in establishing a reasonable belief in consent. In McDonald's case she came back to the hotel with him, apparently voluntarily - her conduct might indicate that it was reasonable for McDonald to believe she was consenting. It's not difficult to distinguish that from Evans who came to the flat later, the only evidence given that she consented in that case is the defence stating that she said 'yes' and was willing.
The appeals are based on the possibility that she did in fact consent (i.e that she had the capacity to do so and did). This was also an issue decided by the jury who seem to have been properly directed by the judge. On the facts they decided that she was not capable of consent, hence why McDonald had to rely on reasonable belief. Decisions by a properly directed jury are very difficult to appeal, which is why this (seemingly correctly) has not been allowed. The report doesn't say she was unconscious btw.