Stand up for somebody. (Standing Up for Somebody)

1) Whatever you say, I'll stand up for her.
너가 뭐라고 하던간에 나는 그녀를 지지해!

No matter what you say, I will (I'll) stand up for her

2)I've always stood for you but you haven't.

I've always stood up for you, but you haven't ever stood up for me

I'm always standing for you but you didn't.

I'm always standing up for you, but you (have) never stood up for me

나는 늘 너를 지지했지만 넌 아니였지!
which better? T-T
어떤게 더 나은 문장이지?

Both sentences are very similar and can mean the same thing; the only difference is that the second sentence emphasizes that the action is still going on or that it is still happening.

3) you should stand up for your faith.

You should stand up for your faith (Correct!)

너는 너의 믿음을 지지해야만해!