The account will not be affected by the IVA as it relates to a separate entity.
The balance in the account is not your money, it is the company's money, however, if you became the owner of the company's shares upon your father's passing away, then these shares will be seen as a "windfall" which you may be obliged to realise to pay into the IVA. In this circumstance, if the company has value you can't simply give the shares away, but may be obliged to get your shares bought out so that this windfall can be paid into the IVA.
Is the business still running ? Then if so, if it makes any profit, either this can be paid to the director as salary, which could be your sister, this is perfectly OK if she is running it, or alternatively it can be paid as a dividend to the shareholders, if you are one of the shareholders, then you will get the same level of pro-rata dividend as any other shareholder and would be obliged to declare your dividend to your IP.