Yeah, Pat's powers were incredible. Just as a casual demonstration, she altered the past so that she had been married to the protagonist for a year, and made it so Runciter's Associates had lost a major contract. Then, at Runciter's request, she again casually alters the past so that the company now has the contract (as they did in the original timeline), while still keeping her marriage to the protagonist.

She was too powerful for a good plot, in my opinion. The novel doesn't elaborate on the exact extents and limits of her power, but it leaves me wondering why she's working in corporate espionage and not, I don't know, ruling the world or something. Why does she have an interest in lowly Joe? Why is she killed off (or half-killed) so quickly and easily?

I agree with you. I'd rather the plot have seen one plotline through instead of abruptly shifting tracks and rendering the earlier plotline irrelevant.

Right, Pat's powers are a very good point. She is so incredibly powerful, that it's hard for me to imagine how you can spin any serious long story around this, much less a story where she's not even really one of the main characters. It's one of the things that make the book bizarre before the event that we are supposed to think that makes it bizarre (and then the end plays some games with whether that half-life plot twist is really what's happening anyway).

On the spot, I can only come up with a rather stupid analogy, but if stories are carefully mixed and balanced cocktails, then a character that can arbitrarily turn back time for themselves and change things, is like taking that cocktail and pouring in a full bottle of everclear.