This is sort of a complicated answer: essentially, all universes in the multiverse do have a time that is considered to be "current" in relation to each other - they are all moving along a timeline, even if not at an equal pace. However, that current time isn't necessarily the same time that Rita is from, so she could be out of sync with her own universe, meaning that it's actually further down the line.

So, Rita could find that book if you want to have the "current" timeline be advanced enough for it to exist. (Rita would still be returning from the point she left, so the future timeline might be radically altered, but it exists at the moment, anyway.