She may be lying, but the witness testimony doesn't contradict her account. Her description seems to imply that his "go back where you came from" comment was close to the start of the altercation. The witness is clear that she only heard the altercation later.
She is also crystal clear that she did not hear those words spoken by Sparkes.
Sparkes was seen leaving and being followed by Thomas who was venting "go back where you come from". I'd bet my house she's lying, but that's simply my take.
One of our lamented ex-contributors would have termed her a "grifter".
And I still object to the notion that her initial action of using the 10 items or less lane is something she needed to account for in any way. Its a practical policy, not a law. It matters only to the extent that it causes inconvenience to others. At the point that there are plenty of empty lanes and no one has to wait, the rule has no meaning or power.
By virtue of the fact that a "rule" (policy) is posted up then one can be expected to adhere to it, however mundane, for the greater good of all. It's called acting for the benefit of many and not the benefit of one.
The fact that there were other empty lanes muddies things somewhat. Why did she chose this one lane (controversially) when other lanes would have presented her with a blame free solution?
If one decides to ignore the "rule" (policy) then one can expect to be called on to account for ones actions.