I feel like high property taxes put somewhat of a limit on house appreciation.

If you know your market and how to assess a property nothing is off limits.

Contact the local municipal building inspector.

The quality of tenants is usually very low, vacancies last much longer, rent to property values are low, appreciation is lower, cash flow is lower and exit options are limited.

You can blame her all you want but if the building doesn't even allow open house, then she's definitely limited in her options and I'm sure she's trying her best.

However...If I told a bunch of seasoned real estate investors I had some sexy new combo mortgage product pairing that would let them pair a 75% or 80% LTV normal 30YF first with a 20% or 15% LTV second at 15% interest rate to let them buy multifamily investment properties for 5% down, I would very quickly be unable to keep up with demand.So, overall, FHA looks bad when you are first starting out and have limited context.

At that point you have a general partnership and 1065 obligation.If you're doing that, it may be advantageous to take it one step further, form an LLC and write your mother into the operating agreement as the functional equivalent of a limited partner. 

What's the main limiting factor for comps?

In regards to Houston area, Nice neighbourhoods with new mud (municipal utility district) run on average 3 to 3.5%.

@Corey DuttonI think this piece from Fortune outlines the challenges many individual investors expected they would have with these properties: http://fortune.com/2015/09/25/housing-wall-street-investment/It would be nice if these units flowed back into the limited inventory market we're seeing.