If Maizy was the only one from the litter with "Biewer characteristics," which I take to mean color pattern, then no, she is not a Biewer. Biewers are their own breed, and are supposed to bred to other Biewers. All of the offspring should have Biewer characteristics. Do you know what the father looked like? DNA testing should only cost about $80 and would be well worth the expense if you can get your money back from the breeder. You have good reason to suspect that Maizy is not purebred. Here is a link to Wisdom Panel, which does breed testing:
Wisdom Panel® 2.0 | Wisdom Panel
They can distinguish purebred Biewers from Yorkshire Terriers, and can also detect if other dog breeds are in Maizy's background as well.