Want to help a friend to taper

Hi! I have to help a friend to taper. But i dont know how. I cold turkeyed and did not do taper. She is taking Xanax 0.5mg 3-4 times. She is on Xanax for 2 years and the dose gradually increased. I want to switch her on valium. As my opinion she have to start with 20 mg valium. Is this right? How to take it 2x10mg or 20mg at once?

Strongly advise 5 mg four times a day. And stabilise for two weeks but surely Ashton manual says how to switch.

Even Valium has dips. Alter later if comfortable.

Dick