if it possible to extract a private key using Abra wallet, use that private key instead of looking for a derivation.
wallet seed is BIP protocol and if they can generate it offline why they need it hard to recovery why

they cant access to it

They are not the only ones Infinito Wallet give you 12 wallet seed words that cannot be used elsewhere.
You can extract the private key from these wallets
the problem is if the wallet suddenly stops.