You wife will be allowed to switch over to a spouse benefit after having earlier taken her own early retirement benefit. However, if she does as you have laid out she will not get 50% of your benefit, but something substantially less. Let me explain.
Because your wife will not be full retirement age by the time that she takes her spouse benefit, she will not be eligible for the full 50% of your benefit. She would have to be at least 66 years old to get the full 50%. At just a couple months' past age 62, she will receive right at 35% of your retirement benefit. This is because you collect less of a benefit if you take that benefit before reaching your full retirement age of 66.
So, if you will be receiving $1,900 per month, she would only be eligible to receive about $665 per month. And because her own retirement benefit is higher than that, what it means is that she will not be eligible to take the spouse benefit at 62 and a few months. She will want to wait until she is 66 years old and then apply for her spouse benefit. That will maximize the benefit that she will be able to collect.
Then, if you die before she does, she will be eligible for a survivor benefit which will pay her 100% of the monthly amount that you happen to be receiving at the time of your passing.
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I wish you and yours the best in 2016,