To reiterate something Pax said (because I have a feeling this is the root of the issue)
If she is manually racking the slide from locked back into battery, she should not be fiddling with the release lever.
It's one or the other, not both, and I bet it's the attempt to do two things at once that's messing her up.
Secondly, I do have a hazy memory of Sigs having particularly hard slides too move. That said, I could do it. It just takes some umph.
and again, if she doesn't want to shop around for her gun, then she doesn't need you to go buy her one. She's a grown woman, she's perfectly capable of putting in the effort if she wants too, if she's not intrested in putting in the effort, well then, I'd think twice about how intrested she really is. Don't push it.