Ok so we all know the armor and seem to never know it's owner. All we know is it was a female from Vault 101. I started a new play-through and may have found out who it is. This is recovered from the Overseer's Terminal from when you first escape the vault:

"We spent a good deal of time in Megaton, and learned a great deal about the "Capital Wasteland" (as the area around Washington D.C. Is now called) from them. Megaton is a fortified outpost of "civilization" (of sorts), but it seems that Giant Ants are the least of the dangers of this new world. We agreed that it was prudent to return to the Vault immediately to revise our survey plans in light of what we have learned. Lewis and AGNES remained in Megaton to serve as "ambassadors" and continue to collect information until we return". -Fallout 3, Report 2241-02-10, Anne Palmer, Survey Team Leader February 10, 2241

(Sorry, teacher wants me to practice citations)

I believe Agnes, as stated in the document, is the owner of the Armored Vault 101 Suit. But if it is hers, what exactly happened to her?

If you have any information to add or a opinion on what I found, please share.

Likely the Agnes that lives in 101. Prob 'encouraged' to return when the Overseer decided to close the doors again.

She's the right age.

Nope. Date is wrong.

Moira says that the person came in "Ten, maybe twelve years ago?" The date when the game starts is 2277.

Agnes went out of the vault 36 years prior to the game. I doubt Moira's recollection is that off, and even if it was, she seems too young to have been more than a kid during the Expedition of 2241.

I meant in regards to the Agnes of the expedition that was recorded. Possible there was another expedition that wasn't recorded, around the time James and his sprog arrived.

I doubt another expedition. I believe Moira stated that the female was a total noob when it came to life in the wastelands. If there was another expedition it would have been more than one person and likely James, and Agnes would have briefed them on how it is out there.

I am thinking that maybe one of the young kids might have remembered when James and the LW arrived and likely the GOAT exam turned out badly for her so she decided to escape the vault.

I'm thinking that people do escape every now and then. Maybe the Overseer fakes a Radroach infestation as a cover up.

Just did some research, turns out Colin Moriarty talked about some "fella" that escaped 5-6 years before our Lone Wanderer. It could be our Female Vaultie.