I think that there is a great deal of trust implied by the actionably ambiguous statements she uses for AC. In an environment where trust between 'client' and development team is not ideal, I find that empowering the business owner to be more prescriptive with AC to be helpful.

In those situations I encourage AC of the form:

The payment form must contain fields for email address and name.

The payment form just match the visual mockup.

When I post a request with data X the response must be returned as JSON

It helps the engineers know what they business owner will test to validate completion.