It would be much safer to transfer the domain rather than giving access to the gmail account (info here:
https://support.google.com/a/answer/171715?hl=en)
Currently, there are two possible issues.
The person giving ou the loan may have access to any other data on your email account.
OR
You may use a recovery address/phone number to get back access of your gmail password by claiming it was hacked, and you could take back the collateral and default on the loan.
Transferring domains is non-reversible, much like BTC, as far as I know, so you could make it much safer for the lender by being willing to do that.
The account email is
admin@keyboard.coNo extra information, no recovery address or phone number. I could not possibly do it.
Once you secure it I'll have no way to reverse.