Nobody is letting Feinstein off the hook. Democrats have been very lax in their response to these allegations. Feinstein hasn't offered an ounce of serious opposition to Kavanugh's nomination despite having some very good reasons to do so.
The FBI hasn't investigated this matter, and it's quite possible that they could query people who know about the party and were there. After all at least one person came out and said that she heard rumors of it happening at the same time. If more than one person heard those rumors I'd think it corroborates her testimony substantially.
Now you're just throwing mud at her. Never mind that she passed those tests.
Can you just explain to me why you think there shouldn't be an FBI investigation? Everything about her testimony is consistent with sexual abuse victim responses, even including the haziness she has around the details and the
length of time it took her to come public. She told her marriage counselor about it 6 years ago in private, and at that time she had no possible thought of 'torpedoing' Kavanaugh's career with the allegations. She passed a lie detector test and one person has come out to give at least a shred of supporting evidence.
There's no real excuse as to why the FBI shouldn't even investigate her story before she's forced to come forward and testify before Congress, and face exactly the same kind of drilling as you're submitting her to. At the moment she has nothing more than her word, and she's most likely to be bulldozed over and ignored.
https://slate.com/news-and-politics/2018/09/christine-blasey-ford-fbi-hearing-brett-kavanaugh.html