любимица (fem.) is a well liked person or a favourite pet. It's usually used to describe someone, and never as a form of address. For example: "Эта кошка - любимица всей семьи" ~ all family members like this (female)cat very much.
"Ваше смс" is too formal after Sweetie (it's better to use "ты" instead). "Что новый" is grammatically incorrect (wrong case). "Нравится" is ok, but I think a perfective verb would be better.

Overall it's understandable, but a more natural way to say it is:
Эй, любимая (or any other endearment of your choice), мне понравился твой смс*. Что нового?
* or "мне понравилась твоя смска"