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.  

It seems to be preventing buyers submitting offers for some reason.It will be necessary to demo the structure, restore the vinyl siding and replace the gutter on the back of the house.Use my contact info in my BP profile or PM me here.Thanx much.

Can't the funds be held in a separate escrow account until an investor approved purchase is made, to prevent co-mingling of funds?

Seems to me to be extra unnecessary work for the property manager to try to use that law.

Instead of simply moving on, the guy in charge added fake charges to the final statement and abusive early termination fees (despite a contractual agreement that prevents them to do so). 

My suggestion would be to either prevent people who have X number of posts or less from posting on a thread inactive for a certain time period, or have a "Pop-up" box telling them the thread is X months/years old, and are they sure they really want to post? 

But, if title is ok with things and willing to issue a policy, would your underwriting *prevent* the loan from going through because of such a lien?