Madness. Free oil changes were supposed to be free, not buy your own oil then subject your vehicle to those hacks who pick at everything trying to find billable services and end up leaving the vehicle molested. It's not the worst possible outcome but it's close, BEFORE they upsell another oil too!
On the other hand, I get not wanting to take on the burden of documenting the oil changes yourself to preserve the warranty, so I would have just kept out of it and after the 9 free changes, making sure she didn't pay more for their "upgrade" (which in this case, they might have charged without doing anything different at all!), THEN offer her the oil and DIY change it.
If you let innocent people be exposed to non-innocent, the best that can happen is minimal bad things. The average that happens is a few bad things. I'd be more invested in her vehicle to change the oil myself with whatever random oil that meets spec, rather than some *special oil*. The key being don't let the vultures near her or the vehicle.
I'm not trying to stereotype all people at all shops, just recognizing the risks vs rewards for these services that are free... which aren't if it averaged out to bays being taken up without billable hours and parts sold. The shop has to make a profit to exist... just reality.