Opinions are like ...well lets just leave it at everybody has one!

In my opinion, a MEDIUM rat might be on the largish size for a ball only 1000g but it really depends on what their "mediums" are....
Offering her food once a week is fine and not what I consider power feeding. I still have my first ball and she is over 10yrs old and she gets a rat offered every week. Totally up to her on if she eats it or not.

I have OVER 20 balls so my way has to be right!! (Just kidding :)