A good question...
It is quite possible that his widow continued the business, but in the references available to me ( A. Leistikow, Baltisches Silber, 1996; K. Kirme, Eesti Hobe, 2000; A. Reinans, Hobedamärgid Eestis, 2005) there's no mention of it. I think furthermore that all three authors took their information from W. Neumann, Verzeichnis baltischer Goldschmiede, ihrer Merkzeichen und Werke, 1905 and he does not indicate anything in this respect either. There *may* be more information in various documents in the Estonian Historical Archives, I have, however, some doubts: Dr. W. Neumann compiled his list from contemporary documents before all the upheavals of revolutions and world wars, and he doesn't mention J. E. Krüger's widow or anything more than what was indicated by the more recent authors.
I have looked in H. Laakmann's Das Bürgerbuch von Pernau 1787-1889 and I have not found any reference to J. E. Krüger or his widow. This book is, however, the second volume and there may be something in the first volume, not available to me. In this second volume I have found several references to various members of the Harder family, all merchants, for the sake of completeness.