I may be wrong... I thought you didn't *have* to file US taxes unless you actually owe the IRS some money.
So technically, VW wouldn't "have to" file for '06 unless she has a lot of US-income.
But it can be advisable to file every year, for many reasons. For instance, IRS won't come asking why you haven't been filing, then you have documentation about why you didn't owe anything. ALSO, this happened to me, if you suddenly get some taxable income you don't have to puzzle out estimated tax the first year, because you can document that in previous years you didn't owe anything (the IRS rules are that you don't have to file estimated tax if you didn't owe any tax the year before).