So, if your mom has a birthday, the most important thing to send birthday gifts is to express your heart, so that your mom feels thoughtful and touched, and this depends on how well you know your mom's preferences and recent situation.
Clothes, jewelry, skin care products, combs, mirrors, hand creams, etc., although very common, but these are every woman needs, not because mom does not care about these will not send. Children think more thoughtful than mom will make mom touched, she will feel especially warm.
Additionally, if you are studying outside, you can organize your photos into albums and give them to your mother so that she can look at them at any time when she misses you, which is the most your mother will like very much as a gift.
If your mother is not lacking anything, then send her a bouquet of carnations, so that she can receive your flowers in the envious eyes of her colleagues or neighbors and the praise of "your son or daughter really knows what to do". This feeling is better than anything else.
I hope this helps.