I'm a childless SIL/aunt, who also has dogs
and also lives a few hours away from family so don't see family children that often (no alcohol issues as far as I know).
A few thoughts. If other family members don't get on with her/find her difficult, then that suggests it isn't about your DC but more about how she relates to your family as a whole - perhaps she finds your clan a bit difficult to talk to/relate to en masse.
People who have children (particularly under 5s) forget how incredibly noisy and tiring your DC can be. She may genuinely not know how to relate to them. She may well have difficulties understanding their speech if they are toddlers just beginning to talk. She may not have a childproofed house. She could well be very concerned about the interaction of your DC and the dogs, especially if they are not used to small, noisy randomly moving creatures in their space. Every parent thinks their child is well behaved in company - unfortunately this is not the case.
She may find it difficult that every adult conversation is either interrupted or is entirely about the latest wonders of PFB. Not every woman is particularly enamoured of DC, nor should they be.
Also you seem to be giving her husband a much easier ride. Why is this? Why are we so critical of women who don't gush and coo over small children, but men get given a pass - "I'm sure he'd be keen if she let him". FFS, he's an adult - if he wants to, then he will.
You clearly don't like her, and you sound patronising and judgemental in your views of her. I'm sure this comes through when you meet, and she may well have given up and thought she shouldn't bother with smug mummy.
Of course, she could also be a rude, ignorant cold person - in which case you have a decision to make about how much time you spend with her.
And why mention that they (as a couple) haven't bought presents? You say this doesn't matter, but if that were true then why mention it? Again, her DH is just as capable as buying gifts as she is - so why is this her fault? Do you/your family measure how people feel by the gift they give? If your DC are very young, then there is no way they will know or remember who has given them gifts. At that age, it is all about impressing the doting parents. For all you know, they could have started a savings acc for your DC, or be struggling financially and can't afford to buy gifts, or perhaps they just don't choose to - it's not a hanging offence.
Without knowing more, think you are probably BU.