
As it is a low grade murmer and she is so young it may well go away. Boxers certqainly can be bred from with Grade 1 murmers.
I sold a pup to a couple (an as far as I know my breed isn't prone to t6his problem), and got the fright of my life, as it was taken for its first jabs at 8 weeks, and the vet could hear a murmer. Two weeks later there was no sign of it when she went for her final jabs. It could well be that more baby (innocent murmers) are being picked up with pups having their immunisations a week or two earlier than previously.
As menetioned above, even if the murmer persists at grade 1 it will never likely cause her any trouble. My freind has aaa Dobe that has just had her 13th birthday, and she has had a heart murmer all her life and outlived all her other dogs, despite a Thyroid problem, and being ridled with cancerous masses all over her body. She was expected not to last 6 weeks 18 months agpo, and isa still happily pottering aroun, her autocratic grumpy self, and still plays with her toys, and demands her grub, and a walk (though it is only around the block)!