That is not an unusual question - in fact it is one of the first questions that beneficiaries typically ask. (the other being how much the adminstration is likely to cost). Both are a little tricky to answer because they are so fact specific.
 
There is no set timeline for the administration of an estate - but there are a lot of different factors that come into play: Did the decedent die with a Will or without a Will; In what County will the probate occur (some counties are MUCH more backlogged than others); what type of assets did the decedent hold; will an estate tax return be required; do the beneficiaries all get along; will the estate have to file income tax returns; is there real property in any other state; is the estate liquid - I think that you get the picture.
 
In general, creditors of an estate have one year from the date of death to file a claim - so typically we plan on about 12 to 18 months from start to finish. In certain circumstances, it may be appropriate to make interim distribution from the estate to a beneficiary - but generally it is faster and cheaper just to wait until the process is complete.
 
As you may have read here in the past - the probate process is intended to be transparent - meaning that no beneficiary should ever feel uncomfortable asking questions. You should call your sister up, ask her if she needs hand with anything (trust me when I tell you that she will be feeling a little overwhelmed from time to time), and ask her how everything is going. Just don't skip that important middle step of offering to help!
 
Hope that helps - Attorney Peter Bernardin