First, thank you so much for your compassion in carrying for those puppies after your neighbor's tragic loss. Pets are like children in my family so I am sure your neighbor is deeply grieving.
As for names, what about naming them after famous boxers/fighters since they are all Boxer mixes and undoubtedly have a will to survive without their mother? You could name the little girl "Laila" after Laila Ali and then come up with names for the two little boys. I am not a boxing fan, so I don't have any off the top of my head, but I think "Laila" is pretty cute.
Thanks again for your big heart!