Besides, if she made it seem like either this new series or the previous series was just a "possibility" it would cheapen the whole series.
Exactly... It would have to have actually happened at the same time...
Although, how would they get the morphing power? The only blue box was with Elfangor, and the Animorphs recovered it.
The Dome Ship is gonzo, so it can't be in there.
That's why there'd have to be another Andalite encounter, and another breaking of the law of Seerow's Kindness... Sure, it's unlikely to have happened, but isn't the truth sometimes more amazing than fiction?
Also, I can't think of any examples off the top of my head, but wouldn't it be really awesome if the writers of the new series interweaved events to subtly coordinate with the original series? Nothing so overt that the two groups would suspect each others' existence, but still things that fans like us would catch and point and laugh our heads off in awesomeness... *sigh*