This actually aids in preventing fraud vs the mortgage system.  

What are others doing to prevent them from freezing?

Just want to offer you my 2 cents in case it helps prevent any down the road problems.

There is some special terminology for sweat equity partners in an LLC which would prevent triggering a weird tax event since you don't have any money in the LLC but are eventually getting something for it.Always get everything in writing, including details on what happens if you want to sell, someone dies, etc.Good luck!

Also make sure to budget for some preventative maintenance (this isn't just for older homes), driveways, roofs, hot water heaters, furnaces, and AC's all go bad even in much newer homes. 

Take a look at the link; I think this will prevent most foreclosures which would otherwise come into fruition, so I actually would not bet on a mass foreclosure problem in the government backed loan market.

In some cases it can prevent you from catastrophic loss but for some cases people may only want cash value or functional replacement value. 

Can the current moratorium prevent them from moving if I as new owner want to move into a unit?

If you have 5 to 10 homes in your portfolio, it is possible to get a mortgage, but it can be difficult.In 2009, Fannie Mae increased the maximum financed-property limit from four to ten.Most banks won’t offer a 5-to-10 properties mortgage because the process of underwriting the investor’s mortgage application can be very hard work.To finance a home via Fannie Mae’s 5-1o Properties program, there are many criteria that must be met, including a minimum credit score of 720, substantial down payment requirements (for purchasing) and equity (for refinancing), no bankruptcies or foreclosures in the past 7 years, and more.Real estate investor mortgagesIn 2009, Fannie Mae rolled back a mortgage rule that prevented real estate investors from financing more than 4 properties at once.At the time, investors were limited to 4 properties financed, which included their primary residence.Today, the maximum number of allowable, simultaneously financed properties is 10.

. $100 a week is not too much to ask, it shows she's making an effort, and it prevents her from getting too far behind in rent.