Quick answer from me: Team Default, unless as Topaz said, Becky and Susan had already confirmed they'd be in the April 1 lineup. Even then, 12 days is A LOT of notice to back out. Merely knowing/speculating the captain wanted them in that lineup isn't sufficient to overcome the fact that there could/should have been 10 other possible candidates.
But the more intriguing aspect for me is that both strong players were on both rosters that would play on the same day.
Around here, the only scenario where you'd have play on the same day would be if the players were playing "up" in our weekend league...and that wouldn't fit the hypothetical description of "strong" players (they'd only likely be considered that "at-level"). Another weak possibility would be the partners being in the 18+ and 40+ leagues with some league season overlap...but that's a stretch.
Our weekday teams play on specific days according to NTRP and the only overlap is for makeups (which are supposed to be played on the "alternate" days of Monday and Friday...to avoid both player and court availability conflicts). I know ya'll don't do it that way up there though.
So...Cindy, how is that this pair came to play on two different teams that play on the same day? Is this a case of said players being in different Districts?
All that said, this highlights a real problem for captains who have players on more than one team in the same league/season. It's generally a recipe for disaster. And, as a player, I won't do it again...even though those weekday teams played on different days and I never had to pick one over the other, it was still more logistical stress than I wanted.
A 3.5 masquerading around with a 4.0 mask on.