My father recently passed away and left approx 100,000 to my brother sister and me.
However my sister is the executrix and seems to think anytime in the last 15 years that my dad wrote me a cheque that it should be deducted from my inheritance.Onetime I signed a letter that I agreed to have a $6000 sum deducted,as it was fairly large.I don't mind that one.
Can she do this? Alberta is the province

Usually there is a paper trail as to what his wishs were and that should tell you who gets what. If not then you need to check the laws where you are for succession after death. ( sorry to hear you lost your dad ).
The law may give you a clue as to division of estate. Other then that try to remember that in times like these it has split many a surviving family for years. Please be careful with what's said and done because your siblings are way more important then money.

Nomrally not, it sounds like you need an attorney to represent you in this.
Sad when family starts fighting over money.