SDIRA purchase from sibling

[Tanya H.]

My understanding is that a sibling is not a disqualified person.   

So with that, I am wondering how/if I can buy a property with my SDIRA from my sister that she bought from my grandmother.  She did not purchase it using an SDIRA, obviously.  

Is there a period of time that I need to wait before I can purchase it with my SDIRA, given that my grandmother is a DP for me?