As you said, the VISA requirements strongly request you to get refundable tickets. But T=there are NO requirements for not changing your mind and cost reducing the trip to non-refundable tickets or finding a more ideal tour. In fact, they probably expect you to cancel the tickets and get better ones once your VISA is approved. People are always adjusting or changing their plans, that is the whole purpose of refundable tickets.
It is not a lie to tell them during the interview "I booked these flights and airbnb because they were refundable as required for the VISA. But after I get my VISA approved, I will probably change them to the following non-refundable tour and plane tickets". Totally honest. You are right, if she lies or gives the appearance of a lie, she could be denied. Just be totally honest, if they even ask.
If she has her green card, an employment letter, and a long-time job, as well as a guarantee letter from you to back up the support for her, bank statements with plenty of extra money, medical, and travel insurance, .. AND no history of visa fraud or issues, then there is little risk anyways. My Filipino fiancee, before she even had her K-1 visa, no green card, still in the Philippines, etc... and without a job or any money, got a multi-year multiple entry Canada tourist visa in less than a week because I provided the financial guarantee and photos of the engagement, we gave some itinerary plans without any bookings. She didn't even need an interview. So if she is financially secure, with a green card, it would be surprising if she is denied.