What you are describing is almost exactly what I myself have been experiencing so perhaps this might help her with the circulation problems in her legs.
Like your sister, I also am a Type 2 diabetic, and for several years now I have experienced coldness and poor circulation in both my lower legs and feet.
At each of my 6 monthly diabetic reviews I have always mentioned this and on each occasion they have they detected either a week pulse or no pulse in my ankles and this was never followed up despite my mentioning it to the at every oppertunity. Christmas was for me a dreadful time as for some reason my toes reddened and started swelling and I experienced severe difficulty in walking particularly when putting the front pad of either of my feet on the ground, so in consequence I ended up having to walk about on my heels solely to relieve the intense pain.
I wanted to see my GP as soon as possible to see what could be done, but after the Christmas period I was informed that they were so busy that the next available appointment would be in 6 weeks time.
Six weeks of walking in painfull agony was something that I couldnot stand, so I did my own research and found that of all things, 1/2 a teaspoon of Baking Soda dissolved in Orange juice (To take the horrible taste away) did the trick, and within 3 days I no longer needed the self remedy and I was more or less walking about with vitually no pains in my feet or lower legs.
Since then I have been taking a sprinkling of ground Ginger dissolved as best it can be in a small glass of 'Diet' coke each evening and I can say that since taking the Ginger everyting has remained fine and pain free.
I did eventually get to see m GP who arranged for me to go to my local hospital (My appointment was in July 6 months after I cured myself) where the circulation within both my legs was examined using an Ultrasonic (Colour) scanner which shows the blood as it flows through the arteries without the need for any invasive surgery (Very Clever)
The result of this was to show that the coldness and poor circulation in my lower legs, ankles and feet is caused by the constriction of the smaller blood vessels (Apparantly a common problem that we Type 2's can experience) and by using the 'Ginger' it would seem that I have obviated the necessity for any operations or stents being necessciary.
I'm not saying or advising that your sister should follow what I decided to do myself, proper professional advice should always be her first approach but as her problems seem to be so identical to those I experienced at the begining of this year I decided to relate my story.