So she found the ruin at the bottom of the Eastern end of Lake Ilinata, and after clearing a bit of rubble, opened the door beneath it. There was a small ruin that just needed a bit more rubble moved out, and would be quite inhabitable.
I'll be stealing ideas from Arthmoor's Volkihar Castle cleanup, and using rubble piles as activators to clear rooms, except that I'll take it a bit further with the way they block the room, and there will be Hearthfire workbenches in the resulting empty rooms. You'll make the furniture in the same way, but you won't build the house, you'll just dig it out.
So far I have:
Underwater entrance to suit an Argonian.
Nice damp ambience, with roots and moss in the main living areas - greenish lighting.
Kitchen and Armory/Forge are clear of roots and moss and have regular yellow candlelight / orange forge glow.
Rooms are:
- Partially flooded passage with stairs up to entrance hall
- Entrance hall/dining room which connects to
- Armory/forge
- Kitchen
- Bedroom (large enough for parents and kids)
- Bedroom connects to
- Enchanting lab
- Alchemy lab (with secret door to shore exit)
- Secret passage to shore exit.
I've connected to rubble and clutter in front of the underwater door to a parent marker which will all be disabled by the quest that gets you the ownership. I want to do something similar to the Orc one, where you do a number of "favor" quests for Argonians to deserve the home, as well as doing all the building, but I'm not sure there are enough of those. Rescuing Derkeethus, of course, but what else?
I haven't yet Nav-meshed the interior, or placed the log for the shore entrance. I still need to add a lot more clutter, including the bookshelves, weapon racks etc. that take so long to connect up. And I can't show you any screenshots until I get the new server built.

It turns out that there are only six available quests that will count. Three in Riften (not including From-Deepest-Fathoms!) and three in Windhelm docks. They include some theft, but no murders. I'm thinking only two needed this time, instead of the five for the Orc Stronghold, where a lot more were available, especially mining.