Close Enough for Government Work?

Action by the government against D for collection of unpaid taxes. D asserts the statute of limitations as a defense. The government contends that D is estopped from pleading the statute of limitations because she executed a written waiver of the limitations period, as specifically authorized by 26 U.S.C. §§6501(c)(4) and 6502(a)(2). Ddenies having executed the waiver.

At trial, the government cannot produce the written waiver. W, an IRS agent, is called to testify that the waiver was destroyed according to standard IRS procedure. The government also offers evidence of the normal practice of the IRS, which, it contends, establishes the likelihood that D did execute a waiver. D objects to W's testimony and to the introduction of the government's other evidence.

What ruling and why?