worried about sister in law? need opinions

So a few months ago now they adopted a puppy, and he got REALLY sick at the beginning, too, and almost died, so my sister is pretty attached to him. But as a dog owner myself of many years, I see some things that make me feel like she might have a bit of an unhealthy attachment to the dog. Their lives very much revolve around the dog when they go out, and while it's gotten better, they wouldn't leave for more than an hour at a time without bringing him. She doesn't let him out of her sight pretty much ever when she brings him to the in-laws' house, and if they crate him (several feet away) for all of us eating a meal and he cries for more than a couple minutes, sometimes she'll go over and eat next to the crate instead of with all of us. Now I don't really know much about crating dogs as we've never done that with mine, so I can't really comment on much, but I can say that the contrast between her response and her husband's is pretty stark. To him, he's a dog; he'll be fine. To her, he seems almost fragile and breakable. 

Tonight we were at the in laws place and there were some big storms moving through; the dog was in the crate at my sister/brother in law's home for a few hours while they were visiting. She ended up leaving to go home before they were slated to go because "her baby boy needed her." I know it sucks for dogs to be left alone with the thunder but he was in fact perfectly safe inside! It's actually those words she sent me tonight that have prompted me to write this post asking for input. I've seen enough of how she acts regarding the dog to see a pattern, but now I want input about how I should think about it. 

It's a noticeable fact that the dog is a placeholder for a child, the closest thing my sister can get at this point.  But my question is, is it healthy how she acts regarding this dog? It's heartbreaking to see the pain she so clearly goes through, and I know that she knows darn well that he will never be a child. But she does get him as close as possible. 

And I notice that this isolates her further from the family (she's pretty quiet until you get to know her as is). It limits how much time they spend out, limits the attention she can give to a guest who's at her own house (constant eye on the dog and running after it; she doesn't really much just let him run free and do what dogs do, but rather seems to need to train everything he does), and isolated her from family when she's visiting and brings the dog, as she has to keep constant tab on him and watch him and be with him. She treats him like he IS a human child instead of the dog that he is. He does seem somewhat stifled as well as a dog in his own development because of it. He's under constant watch instead of just being a dog. 

I want to be clear that I am in no way judging my sister or making light or making fun of her struggle. It breaks my heart so much to see her suffer so much in want of children. I don't know if this dog is actually a good thing for her. All I know is these are some patterns I've been noticing over the last several months and I do worry about how isolating this is. Is the other behavior unhealthy? 

I'm asking primarily for input from those who have experienced a similar situation either themselves or witnessed another loved one or friend exhibit the same behavior. Has it helped or hindered the person in the long run? Does it enable a delusion that isn't really fulfilled? Does it truly help someone cope? Did it isolate? I just don't want to end up years down the road and find my sister in more heartbreak and complications than she had before. If I should perhaps open up to her about being a little concerned for her then please let me know. I just need input. I love her so much!