It all depends on if the tournament is sanctioned by one of the associations. If it is sanctioned, is your DD already rostered to a team within that association? If your DD is not sanctioned on a team in that association and her current team has no intentions get getting into that association this year, then she should be ok by subbing.
Most of the younger age group parents are totally unaware of the rostering restrictions. It is part of the travel parents learning curve. They depend, and rightfully so, on a coach from their current organization to inform them of these rules. However, when you have coaches who are just as green as the parents, it is the blind leading the blind.
Now, if a coach asks you to sub on a weekend and he tells you that for that weekend, your new name is (Insert any name besides your own), then run away fast.