I bought my wife a purs... handb... well, I think they called it a "shoulder bag" on Endless a few weeks ago. I can tell a "clutch" from a "hobo" (now that I know that some purses are called "hobos"), but beyond that they're all purses to me. But if you work in loss prevention, as souperdave does, you have to know the merchandise. (And you also tend to view the "I'm innocent" stories with skepticism, as virtually all of the stories LP's hear are false. The "I don't want to bother the person who could prove my innocence" line is, to put it mildly, overused by people who are guilty.)
It's time to bother your grandmother. You didn't mind bothering her enough to find out that she paid cash, or that she doesn't have a receipt, so how is this really any more bother. If you intend to present that story in court, your lawyer presumably already has her on the witness list. It wouldn't hurt to have the witness who reminded you that you were going to get a purse for Christmas, as well, plus the cell phone records to establish that the conversation actually occurred.
Your lawyer should have tried to obtain copies of any video in advance of your trial. I expect that, if there are videos, your lawyer has copies or can get access to see them.

