In short - get your license.... it's worth it to prevent the pain and hassle of defending yourself in an investigation.At times this business is awesome, and other times it's not incredibly fun - so no matter what niche you pick, you always have to figure out how to mitigate as much risk as you can... and the sandwich scenario you mentioned is fraught with more risk than walking into a room full of angry hornets naked.

Well, if a client of mine sent me a message regarding that type of problem there would be several factors to consider:1) replacing the broken pipes a) what type of pipes am I replacing2) are all of the ceiling joists in good shape3) what areas need to be dried to prevent mold?

Also looking at what preventive maintenance can be done to help reduce future large maintenance expenses.In regards to building relationships, I have a post coming out soon titled Successful REI Takes A Team: Our Roster.

He has not put up a "For Lease" sign outside the building or advertised the space on his firm's website (possibly to prevent offers from other brokers). 

No way to know EVERYTHING when you close on your first deal, but if you know enough then you can hopefully prevent major pitfalls.2.

An insurance policy does not prevent you from being sued and losing your assets.

I want to prevent the buyer (who is an agent) from moving forward on the deal without me.

Here is an example from our property rules:APPLIANCES.Appliances included in the rental of the premises, as noted in the rental agreement, such as a refrigerator, range, dishwasher, clothes washer or clothes dryer, belong to Landlord.If Tenant wishes to use these appliances, Tenant agrees to use them properly in accordance with manufacturer instructions and assumes all responsibility for their care and cleaning.In the event there is a malfunction of an appliance or an appliance is in need of repair, Tenant agrees to notify Landlord in a timely manner and in writing.If Tenant wishes to use their own appliances, Tenant agrees to contact Landlord in advance to obtain prior written approval and instructions, as the removal and installation of appliances must be done with care to prevent damage to the appliance and/or building.Relying on text messages for official communications is not a good way to go.

Is there any laws that would prevent her from doing so?

Many other investors are using yellow letters which it likely preventing you from standing out from your competition.