RootsChat.Com

In 2018 a collection of 16,000 postcards of Lincolnshire was sold at auction
https://bid.johntaylors.com/past-auctions/srjohnt10050?items=Postcard

Of that 10,000 are now in the special collections of the University of Lincoln, cataloguing is (according to this) still in progress. No mention of your mill in the catalogue so far but it might be worth asking as the original owner seemed to have them well organised going by the auction photos.
https://guides.library.lincoln.ac.uk/specialcollections/davidrobinson

S_L

Is the 45 miles apart on the day of death an assumption? Wondering if the deaths could occur in the same place but be recorded where the two ladies had lived rather than where the incident occurred.

S_L

Unfortunately I don't have full access so you only get to see brief snippets of text, selecting Abra as a periodical then searching in it gave these results. The link is to page 2 of the results. Abra volume 32 mentions the sale of the props.
https://askalexander.org/search/middleton/directory/96-Abracadabra/start/10/sort/rel_desc/

To select individual periodicals go to browse at the top of the screen then from the page displaying everything that's available you select the title and when it displays there's a search option for it.

S_L

p.s. for reasons best known to those responsible if you decide you need a subscription to the site for full access then it appears they are found in the store on conjuringarts.org

I didn't suggest the Wintergarten based on the handwritten word. Given the quotation marks I suspect that the word before gardens is something like Peerless or Lawless though I haven't encountered anything similar so far.

Beginning to wonder if newspapers in German are the best approach (unless the original poster knows INO was on tour and where). Considered British newspapers for mention of the performer having recently returned from the continent (to try to narrow down the date), English language magic magazines (e.g. Linking Rings) or their German equivalent (e.g. Die Magie) for passing mentions.

I did find an archive of photos of stage performers at the Wintergarten but sadly the only magic act was an illusionist called Recha.

S_L

Possibly the Wintergarten varieté, Goebbels reportedly went there in 1936 and was unimpressed by Wilson & Keppel (no word on his opinion of Betty).

Interior shot on page 13
https://www.davenportcollection.co.uk/wp-content/uploads/2020/06/2019-08-EMHC-for-website-FINAL.pdf

Albert Speer mentions Hitler attending the Wintergarten:
https://www.artsjournal.com/aboutlastnight/2015/01/almanac-albert-speer-on-hitlers-musical-tastes.html

S_L