I guess I can't fully answer this unless I knew the context Rosemary was using, but if I personally talked about someone who has a "little compassionate mind", and someone else who has a "big compassionate mind", I would be referring to the fact that the person with the "big compassionate mind" has a lot more compassion, and it encompasses many more people. People with a "little compassionate mind" to me might mean people who are good family members, they take care of their family, their friends, and that's about all they care about, but somebody else who does something really major to help the world, would have a bigger compassionate mind.
Interestingly, just the other day, Nelson Mandela had his birthday. He was 89 years old. This is an example of someone in our lifetime who obviously had a big compassionate mind. Anyone who's going to put up with staying in jail for - what was it, 26 years or something - in order to help millions and millions of people, this person has a "big compassionate mind". So if I was using these terms, that's how I would be using them.
So, definitely, a "big compassionate mind" is superior to a little one.