Porcelain help determine the authorship of the article with a picture!

[Хельга2012]

Really need help ! There is a product of china with a pattern of German origin . There is a stroke of Mueller 's , but I , as a layman , it may not mean anything . On the Internet, found a lot of artists with a rare surname. So I decided to turn to professionals . Help identify authorship, and what value has this thing at least is interested orietirovochnaya value. Dimensions approximately 50cm * 30cm. Thank you in advance for any information ! I hope very much for your help !