Ilse is in the database:
German and Dutch diminutive of
ELISABETH, however in this case I have another theory (see below).
Ilsing: I found this as a Scandinavian male given name. Also in use as a surname.
There are also places called Ilsingham and Ilsington in Devonshire, England. The name Ilsington is derived from the Domesday name, Ilestintona, which may have developed from the old English personal name, Ielfstan, when the village was first invaded by the Saxons:
http://www.ilsingtonparish.co.uk/history.htm
If Ilsington is from Ilestintona, that would mean, that Ilsing is from Ilestin. Ilestin is also used as a surname, no meaning found. Probably there is a relation with the surname Iles, which is of
Norman (French) origin. An interesting explanation of the meaning of Iles you can find here:
http://www.surnamedb.com/Surname/IlesI would guess that Ilsing means something like "islander". And in this case, the name
Ilse would probably not be a variant of
Elisabeth, but a form of the described name Iles.
By the way: here's the story you referred to:
http://www.uncommon-travel-germany.com/ilse.html http://en.wikipedia.org/wiki/Princess_Ilse