My :twocents: says this was not a robbery gone bad, it is a murder, hastily covered up.
I base my opinion on the placement of the headshots, and the coincidence that the murder appears to have happened at about the time hubby left for his overnight stint at pop-in-law's chicken ranch. I have no reason to call hubby's character into question; in fact, locals seem to think very highly of both Donna and her husband. If a person wants to kill off a spouse, what better alibi than to have his/her own parents tesitfy that you were with them all night?
Other information (from locals, not LE), indicates that there were no particluarly regular hours of business at the tack shop. I am actually surprized to find that they kept any significant amount of cash there at all. I would have assumed that they would do plenty of debit, credit, or checks from people they knew. So, why would this little workshop-looking barn attract your average robber looking for cash?
If she pulled a gun and they had fought for it, she would surley have other bruises or contusions, but the sheriff said she had no other injuries, and even then, a robber would grab the gun and run or fire off a quick shot. The killer was precise in the placement of the shots, whis says to me that he/she was not in fear of someone else walking in or attracting attention with the noise of the shots. They knew they were alone, that no one else was in the house or on the property.
(forgive typos--cooking while typing...enchiladas, yum!)