I don't think she'd do that to you. I don't think she'll do that to you.
What's difference between would and will in the sentences above? What's the difference between them generally?
In "I don't think she'd do that to you", you're speaking hypothetically (ie. "is this something that she would do to me?"). In "I don't think she'll do that to you", you're speaking only about the future.
Since the former is hypothetical, the time is not specified. This means that you could be discussing the past, present, or the future with "would". It almost sounds like you are debating whether or not she did do something based on her character.
For the latter, it strictly applies to the future. You can't use "will" like this with the past or present tenses.
Well for one, they answer different questions. The first answers, "Is this the kind of thing she would do to you?" while the second answers, "Will she do this to me".
In general, the difference between will and would is a difference of certainty. "Will" implies a specific action that is going to happen, "would" implies whether something is likely to happen.