She told me that some states only allow one will per married couple,
I've never heard this. Not saying it isn't true, but it would surprise me. I can't imagine the rationale for a state to prohibit separate wills for a husband and wife. It is often essential, especially in cases of second marriages where one or both have kids from a prior marriage.
I'd recommend separate wills, even if they will be essentially identical. In that case the cost won't (or shouldn't) increase much, since your attorney will only have to draft one will, then make minor changes for the other. If the attorney is going to double the fee to include your wife, I'd suggest shopping around.
Just as a reference (attorney prices vary greatly geographically), I generally charge about $600 for a will and powers of attorney for health care and for property for the same type of situation (setting up trust for kids) for a single person. If it's a married couple its $700-$750.
Maybe I'm leaving money on the table by not charging more for the couple, but the amount of additional work required is minimal.