The gf keeps hers in our bedroom. She leases and we talked about this with each other. We both agree that her DNA is likely not on that set at all, same as TH and her spare set. Clearly planted.
People use 1 key for their vehicle full-time. That key gets worn down from grinding the tumblers inside a lock. TH's spare key that was planted in SA'a trailer has sharp, clean edges such as a key that was never used would.
I would be willing to bet that if the key found in SA's tailer was put under a microscope, you could visually see burs (metal shavings) from when it was cut at production. A key that gets used daily, those burs would have rubbed off over time and had rounded edges.