Isabel is a manipulative, mean person SPOILERS
I spent the whole movie blown away by how selfish and manipulative the character of Isabel was written. First, she uses her charm and beauty to cut in the bathroom line in front of people who had been waiting their turn. Then she jets after sleeping together only to return 3 months later and announce she is pregnant When Alex doesn't respond the way she likes, she runs off without leaving any contact information. He chases after her and apologizes for his response due to being shocked. He complies with her requests. She totally decorates his house without discussing it. She finds out his job will be soon moving him back to New York and she absolutely refuses to discuss it. I consider myself a feminist and think women should have an equal say in where the family lives, but from how the movie played out, she didn't do much in the way of work so it would only be reasonable to live where his work took them. She gets angry that he hasn't told his parents that they married after just meeting, but I don't think it was crazy for him to be nervous and to not want to tell that over the phone.
I do understand Isabel being upset when she discovered he had taken a job that would move them back to New York through his boss instead of him, but I don't know how he could have told her without her freaking out. But the kicker for making this character totally unredeamable was her telling Alex that she had lost the baby when she hadn't. What a terrible thing to do -- both make someone grieve a baby that wasn't dead and lying so the father would not be in the picture.
Oh, and I forgot this. At the beginning of the movie when she found out that he was supposed to be moving back to New York CIty, instead of discussing this, she just made her 5 older brothers and her ex boyfriend load him up and take him to the desert to intimidate him into staying in Las Vegas.
She spends half the movie throwing a fit because he wasn't being honest while she was the most deceitful character in the movie. She acts like him being scared to tell her he had to move back to New York is the same as lying about a miscarriage.