She has a heart of gold.
That's like comparing apples and oranges.
What do all these statements have in common? They are all yesterday's news. We've heard them countless times before, and they lack pizzazz.
When you're writing, try to come up with unique sayings rather than relying on recycled thoughts. Devise your own metaphors and similes. Even if they're not as clever as a well-known cliché, they will be fresh. They will be yours, and readers will remember and respect the fact that you took the extra time to come up with something original.