My husband does cabinetry so I ask him your question. He says that malimine really isn't meant for outdoor use. Yet if you really want to use it you'll need to sand it before you paint it. You have to find a way to seal the outside even if the edge is trimmed the seams could potentially absorb water. The only sealer that may be strong enough to keep water out is marine varnish but it will yellow as it weathers. My husband says if even the smallest amount of water gets to the partical core it will expand within a matter of days. Bottom line, this really isn't the right
surface to use for this project so maybe you need to talk to your friend about a different way to make her project.