Oh yes she can. The issue of child support stands alone. When the 'parents (step or not) who BOTH have been providing for the children - as they inevitably do by sharing costs of heat, transport, mortgage/rent, food, clothing etc etc - should those parents split then the courts do not and should not treat the children as inanimate objects with no dog in the splitting up race.
But TimG believes the children have no interest. Only the poor step-parent has a financial interest and the courts should ignore any diminishment of support for the children.
And the supposed 'hypothetical' case referred to above clearly addressed the point. The case was brought before the courts to determine if the non-parenting agreement would stand. The Alberta court rejected such a thing for the obvious reason: the detrimental
effect upon the children involved. INVOLVED - not standing on a shelf somewhere to be dusted off from time to time.