Probably happy; I have a feeling it'd probably be a more definite frown otherwise.
Also, since Alice is ambiguiously the daughter/creation of Shinki in the PC-98 continuity, I'm getting some "oh, hey, Alice, I fucked your mom" vibes from this.
Maybe Marisa sneaks in to have a surprise romp in bed with Alice. She has her way, and when the lights turn on she realizes it is not Alice, and as any comedy goes Alice comes in right after. If so it can go a few ways by common laws of hentai 1. Alice is mad at Marisa for defiling her mother(doubt that one) 2. Alice is angry at Shinki for going ahead with Marisa 3. Alice thrown into utter shock and disbelief followed quickly by unguided anger