I will not even hazard a guess as to your mother's intention. No matter the intention my advice is the same:

1) It was meant as an insult or to get under your skin. Take away her power and lie through your teeth! Tell her how beautiful it is and how much you appreciate it. She gets no satisfaction from your reaction and maybe it will teach her a lesson in being gracious.

2) It really was meant as a peace offering/symbol of your dad's globe. Tell her how beautiful it is and how much you appreciate it.

No matter how you feel about it you will be the bigger person and can hold your head up high knowing that you were gracious and didn't sink to her level IF it is an insult.