It’s entirely possible that I have this wrong. But if I understand correctly, a development player can be upgraded to a regular roster contract at any time. But once that happens, they cannot be placed back onto the development roster without first clearing waivers.
So, just as a hypothetical, if a Sparks player suffered an injury that was going to be week-to-week, Kate could be activated for up to 12 games while still on the development roster. But at any point after or before she has played 12 games they could go ahead and make Kate a full roster player if it looked like the player she was replacing wasn’t recovering as quickly as they expected. But once Kate is given a regular roster contract they cannot move her back to the development roster without risking another team claiming her. Although I think the Sparks would have the right to match that team’s offer.
Clear as mud, eh?