Re: how to transfer Ledger BTC to a new ledger wallet (anonymously)
If your friend's goal is privacy (from an ex or something along those lines,) she can merely send the funds to an exchange that allows HD addresses, like Coinbase. Then she can reset her Ledger with a new seed (optional) and send the funds back. They'll be nearly impossible to trace without a warrant. 
Because of how exchanges are, it won't be advisable, although I understood that exchanges can act like a mixer but they are centralized, and controlled by governmental policies. People's dependent on exchanges makes the government to be controlling people to the extent they are trying to even want to have laws that can make them track individual noncustododial wallets people (citizens) are using. Also the exchange will know the address the Bitcoin is sent to, and some exchanges like to freeze users funds is another reason people should be discouraged from using exchanges for this purpose. The reasons I can not advice anyone to use an exchange for privacy purposes, using exchanges will likely result to privacy invasion and must not be included while thinking of privacy. The best options are to use CoinJoin, like Wasabi wallet do CoinJoin, or making use of mixers, or converting the Bitcoin first to Monero first and converting it back to Bitcoin in a decentralized way.