See post 10, she never “served” in any capacity, and she was never a mechanic.
She most certainly did serve - not as a mechanic, but as a driver - which required her to have basic mechanical skills as drivers were expected to perform running repairs where necessary. The article fairly accurately describes her training - it does not describe her subsequent service which did involve her driving military vehicles all over England. She was on active service from March until the end of July 1945, at which point, following the close of the war in Europe, she was released from active service along with thousands of other women who were among the first to be ‘demobbed’. It was only five months active service, but it was active service. The Royal Family do not claim active service unless they can do so on the same terms as any other members of the service.