If it were me faced with your dilemna, I think I would consider sending her a little irreverent note or card if you can find the right occasion, something light but meaningful between the two of you, like an 'in' joke.
I'd suggest you see what her reaction is and do more of what works. If she is as stubborn as you say, it could be that the small initiative she took at Christmas was more meaningful than it might have otherwise appeared.
