Unless theres some linking evidence its all just speculation, but remember there have been identical crimes, committed before that almost seemed "too coincidental" many times, and they turned out not to be related.
I personally dont think Kohlhepp was responsible for this case, he had a successful business, he was well off finalcially, I cant see him just walking into a check cashing store to kill a woman hoping for a payoff
Kohlhepp, was all about control, that was the underlying theme to his crimes, in the Superbike murders, Im willing to bed that he felt he lost control by trying to intimidate them, when they didnt balk and take the bike back under threats, he decided to start shooting .
IE He LOST control
A psychopath usually does things to gain some form of self gratification,
In this case if killing Small was the motive, then why try to make it look like a robbery? he knows theres cameras, and police surmise he knew the alarm was tripped, and thats a chance for more evidence to be left.
If it was really about robbery why not make her show you where the money is THEN kill they victim after ? , or not at all ?
First thing Id do is leave no stone un-turned in her background, then id look into any similar attempted robberies in the area.