Show her Nexaph, where everything is tested but expensive, especially to ship to the UK.
Then show her the extensive 3rd party testing done by group tests for Chinese vendors. Explain that Cain at Nexaph is buying the same stuff from China, testing it at the same lab in the catch Republic, and selling it at a significant mark up. You could buy and test yourself OR join a group test for a significantly lower cost.
Assure her that you will buy group tested products. Or at the very least, buy from Uther who is fairly cheap (not including GLPs) and tests extensively.