Spouse is concerned that she will not be given the same transfer as a wife who is a U.S. Citizen. My understanding is a spouse is a spouse, but looking for confirmation.
For most people, it works out the same. If you are dealing with millions of dollars, you should be talking to an Estate Planning Attorney, not asking questions on Stack Exchange.
Assets left to a surviving spouse are not subject to federal estate tax, no matter how much they are worth—IF the surviving spouse is a U.S. citizen. This rule is called the unlimited marital deduction. It is in addition to the individual exemption that everyone gets. The marital deduction, however, does not apply when the spouse who inherits isn’t a U.S. citizen, even if the spouse is a permanent U.S. resident. The federal government doesn’t want someone who isn’t a citizen to inherit a large amount of money, pay no estate tax, and then leave the country to return to his or her native land. Still, keep in mind you can leave assets worth up to the exempt amount (again, $5.25 million for deaths in 2013 and $5.34 million in 2014) to anyone, including your noncitizen spouse, without owing any federal estate tax. And if the noncitizen spouse dies first, assets left to the spouse who is a U.S. citizen do qualify for the unlimited marital deduction.
So, up to $5.34 million, everything is fine. If more than that is involved, think about becoming a citizen, and/or talk to real Estate Planner.