Have heard of one of her males but dont know her personally nor the kennel - but they dont breed often and do show and canine sport
There are questions to ask a breeder as listed on Newcastle's site -
Big thing is if they answer all the questions you have esp with regards to health testing, and you agree with their breeding practice and theory on breeding and the boxer, then go for it!. If something just does not sit right, then try looking elsewhere. Any reputable breeder would be more than glad to have a home prospect ask the questions and get to know them better, than someone who does not.
Good Luck and hopfully you will being a little one home!!