Does a US citizen residing in Canada pay the tax penalty for not having a healthcare plan?

AFAIK the requirement is to have a plan while resident in the USA, so no.

The way I understand it, no she will not have to pay a penalty. I see @bolwerk says the same. The old tax laws, I have no idea what they say now ( know they have changed) when my husband lived and worked out of the country was if you were only in the US 30 days or less in a year then you were exempt out paying taxes on the first $75k of earnings. Other tax obligations also are eliminated when a citizen lives outside of the country, but they need to watch how many days they come to visit of they visit, so I think it is important she research the laws well one taxes and penalties. The IRS website has a lot of information and there are accountants who specialize in doing taxes for expats. I recommend utilizing an accountant who works with this circumstance all the time.