@Cameron Marro - I would work to get her out, move in to the bad unit and rent out the good unit. 

The property must be able to self-sustain from the rents received if you are financing using an FHA loan (rents must be able to cover 100% of the PITIMI). this does not apply to 2 unit, and I'm finding that some lenders will use all units for this test (assigning a rent value to the owner occ unit) and others will only use the non-occupied units for this test. its a hurdle to be aware of if you intend to buy MF using FHA. 

There are numerous reasons why they usually do not make good rent properties. 

All rents you get from this property has to go back into the SDIRA but if you get a 20 year mortgage (that the rent can cover) and can pay the rental off by age 65 you will have turned that $90K into several hundred thousand’s of paid off real estate.

that we’ve learned in our 24 years, managing almost 700 doors across the Metro Detroit area, including almost 100 S8 leases:Class A Properties:Cashflow vs Appreciation: Typically, 3-5 years for positive cashflow, but you get highest relative rent & value appreciation.Vacancy Est: Historically 10%, 5% the more recent norm.Tenant Pool: Majority will have FICO scores of 680+ (roughly 5% probability of default), zero evictions in last 7 years.Class B Properties:Cashflow vs Appreciation: Typically, decent amount of relative rent & value appreciation.Vacancy Est: Historically 10%, 5% should be applied only if proper research done to support.Tenant Pool: Majority will have FICO scores of 620-680 (around 10% probability of default), some blemishes, but should have no evictions in last 5 yearsClass C Properties:Cashflow vs Appreciation: Typically, high cashflow and at the lower end of relative rent & value appreciation.

If that's the case investors will compete even harder for these 1-4 units  and basically flip them tax-free by renting them for a little before selling. 

I am currently living in one of the units and renting the other one.

There are really great REI opportunities in different markets - markets in the Midwest and Southeast of the country are particularly lucrative - where not only are the purchase prices reasonable for most RE investors, but the homes are turnkey (new builds or completely rehabbed homes, tenant ready, systems 10 years of life remaining on them, property management teams in place) with appreciating home value AND appreciating rent.

What did you use to pay for rent where you live now? 

You have enough to buy multiple rent properties.