Doubt about would and will in the aspect of possibility

I was told that "would" indicates a lower possiblity and "will" indicated a higher one.

1.I will go to the park tomorrow.
2.I would go to the park tomorrow.

1.I will do it.
2.I would do it.

In the above sentences, the first one means a higher probability but second one isn't.

But I am not so sure about the following, which include the words - "not" or "never".

1.She will not/never do it.
2.She would not/never do it.

Does the first sentence says it is more certain that "she" is not going to do it? And the seconed means probably she won't do it but not very sure?