Anna's mother was Dorothea Christina Reinhardt. She died the 16th of April 1895 and is buried at Elmhurst Cemetery in St. Paul. She is buried under the name Maria. In census records, her name is usually given as Christina.
That is really awesome that you have Frederich's war diary. I hope you will share the info when you are done. Does it have any genealogical info?
Email me at mkbiddy at gmail.com and I will send you some info. I do have a family tree on Ancestry if you have access.