I cannot believe that it has been less than a month since your father's death and you are concerned about the value of the estate! In this period, the ordinary bills have not come due to say nothing about medical expenses. If he had been ill, it will several months before insurance has been processed and final payments made. Handing ordinary bills is nothing like bills incurred for end-of-life care.
Estate tax filings cannot occur until all bills are paid. It is at that time when she will have a good idea about the size of the estate. Check your father's state's as well as the federal requirement for the timing of the filings. If it appears that she will miss those deadlines, then you can worry about the failure to handle the estate in a timely manner.
I can understand your sister's reluctance to make any commitment to estimate the size of the estate from you posting the "I have asked her numerous times..." in less than a month since your father's death. I suspect she fears that if she underestimates it in honest error, you will pursue legal action against her.
It may be the case that everything is in trust or paid directly to beneficiaries so as to avoid the costs of probate such that opening probate might be unnecessary. Remember that the costs to probate the estate, attorney fees and executor/trustee fees come out of the estate before it is divided. It may be in your financial best interest to try to minimize these fees in order to maximize your inheritance.
As a final note, had your father wanted you to have detailed information about his finances, he would have shared that with you during his lifetime. He chose your sister to administer his affairs; you should respect that and not appear so greedy as to be looking for your inheritance rather than mourning his passing. You are being unrealistic in your expectations and demands.
Remember, you can always file to open probate yourself; you may not necessarily be appointed executor; you will alienate your family by pressing the issue if it is unnecessary.
Since many of the attorneys on this forum seem to be taking the day off, you might wait until later to see if they have legal advice for you.