In older times there were often different ways in spelling a name, without any special reason,
later in time names stayed the same. (in older times it was often written as the pastor or officer heard it, after about 1811 /beginning 19 th century names became more in one way written )
Guurtje van Ingen had a sister, Maartje or Marretje van Ingen and she first married to one of my ancestors in Nijmegen. Later she remarried, after the young death of my ancestor)
They were daughters of Alert/Aaldert van Ingen and Jantje Peters (van der Veer), born in province Gelderland.
Nice to read about your story, you've come a long way with Slingerland !