I'd have to think that if young Rydia was meant for the later portions of the game, the port would've added her in.
The point of the ports was to leave the original game unmolested for the most part...
Then again, I wouldn't be surprised if TOSE thought that giving her armor would be nice, only to later discover "holy crap she's not in the game anymore!" You'd think they would know, since they let you choose whoever you wanted once you got to the end.
TOSE had nothing to do with the original game.

The game has a complete set of data for each character and their armor equippability (unlikes most games where characters you never see again have limited equipment choices, like Lufia 1 or Dual Orb 2 or other RPGs I can't think off the top of my head).
What TOSE DID do in their port was remove all references to the unfinished stuff that was in the original game (see a number of my patches that added them back in), which also included the Yang-to-kick DK (not Paladin) Cecil's ass or Rydia learning Cure2/Cura. That's not what I'm discussing.. I'm talking about the original FF4 details. I'm starting to think FF4ET's rebalancing (well, it includes the Minerva Robe, although the Ribbons are overpowered) was more of an intentional tweak. Other than being easy... the "final" save location in FF4ET was a logical position for a save spot... yet it didn't exist prior!
Anyways, I'm just thinking out loud at about a small detail about this game's unfinished factor...