What can I do to help her not to die?
First step is to identify it - could it be a peace lily (Spathiphyllum Wallisii)?
Repot it straight into that white pot. Stop watering it so much (or start watering it)! I water mine about once every three weeks.
Hmmm, I don't think the white pot will have a drainage hole ..........
If it has been overwatered and roots have died off it would probably be a good idea - after re-potting into a pot with drainage holes! - to cut off about half the leaves so the remaining roots can cope.
The problem with decorative pots is that they don't tend to have drainage holes, so it's best to use the same method as you're already using - a plastic pot inside the pretty one.
It looks like it's been a bit too wet. It might benefit from repotting into a bigger pot, but even if not, and it's staying in the one it's in, make sure there's a little layer of gravel in the base of the white one to avoid having the plant sitting in water. I'd use some fine gravel (same as you would put in the base) to finish it off on the surface, rather than the big pebbles.
If it needs moving into a bigger pot, you'll probably have to buy a bigger version of the white one too, as that one wouldn't accomodate a bigger plastic pot.