We've had this happen to us but it was a late comer that asked to join. Most of us said yes, not a problem. Our organizer was a firm no and then got mad when we said we'd just pixie dust her family. I'm glad we included her because she really went all out on her gifts.
We've had it the other way, too when someone asked to join last minute (like within 2 weeks of the cruise) and the organizer added her. I made more gifts for her family. At our group meet, she showed up and was very apologetic but she didn't have time to get gifts this close to the cruise but anyone who wanted to meet her at a certain time, she'd buy them a drink (we don't drink so passed on her offer). But she made it very clear that she still wanted our gifts because her kids were looking forward to it. Right or wrong, I pixie dusted her and her husband's gifts to another cabin but did leave her kids their gifts because it wasn't their fault.