My sister has power of attorney for my mothers estate. Is she obligated to show any of the transactions she has made?

If your mother is still alive, generally a person with  a valid power of attorney does not need to provide an annual accounting of the handling of your mother's financial affairs. If your mother is mentally competent, she has the right to revoke the power of attorney at any time. If your mother is not mentally competent and you suspect wrongdoing on the part of the person handling your mother's financial affairs, it would be best to check with an estate attorney about what your rights may be with filing some type of a civil action against your sister to have her removed as the power of attorney over your mother, and instead, perhaps, to have a formal legal guardianship where the court would oversee the handling of the estate. If your mother is deceased and instead there is a pending probate with your sister acting as the personal representative of the estate, if a formal probate,  a final accounting has to be provided as part of the probate process. If you again suspect some type of financial wrongdoing on your sister's part as the personal representative of the estate, you would have the right to file some type of probate action to have her removed as personal representative for good cause. Again, it would make sense to consult with an experienced estate attorney on such issues.