I would like to say, "She's so full of life". This is to mean she's energetic, she lively, exuberant, loves to live life.
I came across two idioms: 生气勃勃 and 生机盎然, but from the examples I've read, 生机盎然 seems to be used to describe nature more often than people. If neither of these are good translations, what would be more suitable?
You can use 活力 (vitality/energy), such as:
充满活力
活力四射
活泼 usually used for someone's character, means outgoing, optimistic. While 活力 just means energy/vitality, so you can say 充满活力 for full of energy, or energetic, or full of life.
I think neither of the idioms you propose works for people.
A common word is (很)活潑, usually translated 'lively' but used mostly to describe someone's personality, with characteristics such as outgoing (外向) optimistic (樂觀), etc. If you want a chengyu-like expression, there is 活潑可愛, but it is not as widely applicable as 活潑 by itself.
An antonym tfor 活潑 would be 沉穩, soft-spoken, reserved.
If you mean someone with a lot of energy and spirit you could try 精力充沛.
Another possibility is (很)熱情; this is can indicate both enthusiasm and warmth; being friendly to others, and enthusiastic about life's opportunities. Be careful with this, though, because it sometimes means 'passionate' as in romantic matters too. 熱心 is perhaps safer, though less, um, passionate. If you want a chengyu-like expression there is 滿腔熱情.
A somewhat colloquial translation occurs to me:
她真是精气神儿十足。(She's quite lively. )
Where 精气神儿 is a colloquial word, loosely for "life", and 十足 is the translation for "full of".
