Sounds like this is already a "retirement" fund of some flavor. You acquired it with money from her pension buyout. As others have stated, you need a professional involved here, and it's very likely you can't add or remove money without fecking something up. You could DIY, but the potential tax consequences are enough that I'd involve a professional.
If you really want to buy more of that particular fund, you can likely buy it at any of the retail brokers. Vanguard, schwab, etc. I'd guess. I"m not familiar with AOMIX.
If it were me, I'd just open a second account at the broker of your choice, and buy some of that fund and call it a day.
I think it's important to realize, there is a downside risk to that fund, as there is with pretty much all of the various mutual funds out there. Looking at it's all time chart, it looks like it has dropped about 50% once, and 20-30% a few times. Yes, is has also done well over time, but depending on your time horizon for the funds in there, your money is at risk. Can you tolerate a 50% drop and still build your house? The only thing certain is that you can't time the market. No sense in juggling knives...
For a house savings, I'd look at some of the high yield savings CD's our there. I like Ally, but there are lots of others. Your local bank may even have an offering. Sometimes, they will match what the big online places are doing, just to keep your $ in house. But you have to ask.
There are also true, money market accounts. They will be around 1.00% though. https://www.ally.com...market-account/