You’re describing a mother who’s passive-aggressive, not emotionally absent. Giving the silent treatment is a common tactic of those who show hostility in an indirect way. Your mom is mad at you for not giving her a gift. Instead of communicating her hurt and disappointment, she’s punishing you with her silence. She’s not emotionally absent; she’s angry.
If you look at your history with her, you’ll probably detect a pattern of passive-aggressiveness. These folks have low self-esteem and lack the ability to communicate in a straightforward manner. Common passive-aggressive behaviors include sulking, pouting, being sarcastic, complaining, playing the martyr, and giving the silent treatment.
Passive aggressiveness is a stubborn trait and these folks are unlikely to change. You can choose to ignore her retaliation. You could also choose to show compassion, though, by acknowledging her hurt feelings. If you typically send her a Mother’s Day gift but didn’t this year, you should certainly appreciate why she’s disappointed.
I hope you two resolve this soon. Life is too short for this to keep you apart.