Has sister spoken with oncologist or pathologist about various options? any family history? There are number of 'targeted therapies" for AML and it would be worth her considering DNA testing options. Especially given age of onset and already having presented with two different primary malignancies, its possible they will find well known cancer syndrome gene(s) alterations, among other 'acquired' ones. Some, such as IDH1, DNMT, BCL2, FLT3 are targetable 'drivers' for a number of tumors, including AML. At least one pathway called the "Fanconi Anemia pathway" (includes the popularized 'BRCA" genes among others--FANCA, FANCD, PALB...) has strong evidence of involvement in both breast and AML tumors and ensuring the genes involved are part of any test ordered would be important in your sisters case based on her clinical history. There are drugs that interfere with the specific pathway biology to varying degrees of efficacy. While, to my knowledge, none of the therapies are early-line treatment, there are many oncologists whom argue in favor of earlier testing so that backup management plans can be discussed and fully understood ahead of time--especially because delivery of results can take some time from initial order. Some mutations are also of diagnostic significance and may arm the doctor with knowledge needed to stay ahead of future high risk developments. Just something to consider talking about with the physician, as many oncologists are not up to speed on all the modern tools available (or dont specialize in tumors from all organ systems) and therefore patient questions may probe further investigation and productive subsequent visits, or even referrals.
I wish your family the best during this emotionally difficult episode, and pray the next chapter is yet another victory over her cancer.