Hi Judy61,
A beneficiary to a will does not have any right in the estate until distribution. Before this time, the estate is owned by the deceased (managed by the power of attorney) before the deceased dies, and by the executor or personal representative when the deceased passes. Therefore, there is no express right to see the books of the deceased before distribution.
After paying of debts and expenses, the executor must prepare a distribution report listing out all the assets of the estate, how much money paid to the beneficiary for each estate and how much of the estate was paid toward debts and expenses. This report must be issued to each beneficiary at distribution. This is when beneficiaries check the account in relation to their own asset and see if there are any problems with the management of that asset.
A beneficiary cannot interfere with the management of the estate by the power of attorney before the deceased dies because at that time, the deceased still owns their estate. If you have a problem with how the power of attorney is managing the deceased's assets, you need to apply to court for an injunction on how the power of attorney acts.
In extreme circumstances, where there is obvious grounds to suspect that the executor is squandering the estate assets against the interests of the beneficiaries as a whole, you can apply to court to see the financial accounts and ask the court to demand the executor to account for their actions. However, it is quite rare that courts will grant this.