Not sure how many points you can have before you must ride open. A friends horse has been imported and awarded 37 points and not sure if she can do prelim restricted or not?
Just checked the BD site and it is 37 points for prelim. Also, it states the minimum pointes awarded is 35 for a imported 5 year old, so would check it out.
Unless she goes H/C - then no. Prelim Open is open to non-registered or registered horses, registered or non-registered riders, but must not have gained 37 points.