Maybe rather Grethe (much more common than Gretha, Gretha was rather Dutch and Niederdeutsch and not common in Southern or Eastern parts). One can not make out a real difference between a and e here.
Last name: ?enschert. I see an sch there. The first letter is not going below the line (which it should if it was to be J) but I have my doubts with any other letter as well. Could be a G, but her G in Grethe is different. Could be an A or maybe an L.
A lot of maybes here.