If it can't be planted now, either method could work. Sinking the pot in the ground poses some problems if drainage is at all an issue. The container will not drain as well as if it were above ground with any rain water/snow melt free to drain out. I might prefer the garage as long as you can keep things right at freezing or slightly above. Anything below 26F for any length of time can fatally damage the root system. Bubble wrap works well :-))

Sounds good. I don't know her soil type, and I'm sure she doesn't either.
Bubble wrap it is.

Thanks for your opinion. Always helpful!