Bah, I hate endings like this. Basically, it’s the Narnia ending. “Well, the characters you grew to care about are all dead, but it’s OK because they all go to heaven.” 
OK, technically just Joe and Allison are dead, and Allison got plenty of Joe-less years first, but still.
Even though I disliked the series, given her conversations with dead folks, I can see no other ending. 
I guess Marie was young enough they felt they could use a different actor, Ariel was old enough they felt they could use the same actor, and Bridgette was stuck in between.
But they really should have done more to make Ariel look older. Shouldn’t have been that hard for one scene, where they could make the lighting whatever they wanted.
Here are the oldest looking images I could find of her on google, just to prove it’s possible:
http://www.parade.com/export/sites/default/images/-v4/celebrity/2009/0621/default-sophia-vassilieva-cameron-diaz.jpg
She’d still get carded buying beer, but I wouldn’t immediately assume the ID was a fake.
I liked the ending very much when I watched it, but since then something has been bothering me.
If I understand the concept, Joe appears to Allison to tell her that he’s dead, and she’ll have to go on without him. She lives another 44 years, and then dies to find Joe has been waiting for her. I gathered by her expression of surprise that she wasn’t visited at all by him over those 44 years.
Well, why not? Why couldn’t he have visted her every night – to talk about her day, the kids, the grandkids, the great-grandkids, etc.? Would that have somehow prevented her from moving forward? If she intended to re-marry, yes, I could see the problem, but it didn’t look like that happened. Otherwise that would have been an awkward meeting. “Oh, Joe, thanks for waiting, but…”
Maybe she ran out of long distance minutes?
Good point - but I suppose it could be that she was just “surprised” that she had died and suddenly she and Joe were both young and together again.
How many men would put up with being married to her? 
It’s no biggee; my wife sees dead people. You get used to it.