@PyongyangKipperbang
It really isnt a healthy way to deal with infertility. She needs to accept that she will not have a baby, not treat a pet as if it was a baby. IT isnt good for her mental health, especially as has been pointed out, the dog will only live for 15 years or so.
Treating a pet as the baby she cannot have is not a mentally healthy way of dealing with infertility, and I stand by that.
Who made you God? Who and what gives you the right to dictate to people how they 'deal with fertility?' Or if any one way is 'healthy.'
You sound as judgemental, mean, and callous as the OP. You know fuck-all about anyone else, or their personal circumstances, or how they feel, or their reasons for how they deal with their fertility, OR their MENTAL HEALTH!
So you can 'stand by what you say' til the grass is ten feet high around you; it doesn't make you right. Not even close!
And I am pretty sure the OP's brother and SIL know the dog isn't going to live much past 15-16 years. They are not going to expect it to live as long as an adult FFS! What an incredibly stupid thing to say. (And that's aimed at @Missillusioned too! )
Are you both actually serious?
Surely you cannot be that dense?
You cannot seriously think that ANYone would expect a dog to live as long as a human, and be devastated when the dog dies at 'only 15 years old!!!' 
I thought I'd read some weird shit on here, but this takes the biscuit!
And before you ASSUME.... No I am fortunate enough to have not struggled with infertility, and have 2 children... I know a few people who have struggled with infertility though, and fortunately they don't have people around them like a few callous posters on here. They have kind understanding people in their lives..! I can't believe some of the shit 2 or 3 posters are coming out with on here. Who the fuck do they think they are? 