At least ten years.

She was telling the truth.

as many years in prison as Kavanaugh will get for lying under oath (he should get an extra year just for being a douchebag)

You are delusional. Take your meds.?

How could it ever be proven that she lied? There may be no collaborating witnesses that have come forward, but that doesn't prove she lied, but rather it is a failure to provide evidence that she told the accurate truth, which is different. Also, lies are intentional. If it is a case of mistaken identity or faulty memory that is not perjury. Although, admittedly, the judgment of perjury depends upon a subjective judgment of whether or not people believe you. However, so far it seems nearly everyone has found her to be a credible witness.

Also, if Kavanaugh perjured himself, how many years should he spend in prison?

I have yet to hear a claim as to anything Ford said that was untrue. Given Cavanaugh's background and demeanor, the attack seems entirely plausible. The defense of Cavanaugh by Republicans speaks volumes for the complete mindjob they embrace (Fox agitprop).

Cavanaugh's blanket denial, while emphatic, doesn't displace the unwillingness to take a lie-detector, or to specifically declare that Ford was lying. By his own testimony, Cavanaugh appeared to have lied in his self-representation as not having been an uncontrolled alcoholic. Cavenaugh's extreme partisanship and delusional obsession with Clinton patently demonstrates disqualifying traits (Hence the condemnations by other, real jurists). Thus, he also appears to lie in saying that he can be unbiased; his previous positions and statements contradict this.

The Republicans all step backwards together as far as validating Cavanaugh's claim his accusers are part of a conspiracy. His statement and their complicity are pure slime.

Steamrolling this unvarnished partisan onto the Supreme Court is a record low in Republican behavior, ever and always placing party ahead of the Country's welfare.

Will Republicans adopt the unwanted children generated by nixing RoeVWade? Or will they complain that Blacks are robbing the welfare system?

Will Republicans lose traction with the Evangelicals when the Christians lose the Pro-Life rallying cry?

You can be sure the truth will come out. Dr Ford better retain a good attorney. Lying to Congress under oath is a serious crime. I think the truth is she had a dream and under hypnosis she began to believe it.
However if some of the little details are proven to be a lie, like coaching to pass a lie detector, or even denying knowledge of the Senates offer to come to her, she can be in trouble.

there was no investigation so no way to prove who lied.