Tricky. Considering she was born and baptized before the mandatory registration of surnames with only given name Pietertje and mother's name Grietje Lolkes I would go for LNAB the matronymic Grietjens or Grietjensdr.
There are two 1811 surname registrations, one with Grietje registrating surname Wildschut for herself and the other registrating surname Poppes for "her child".
Pietertje apparently never used surname Poppes. So I would record Wildschut as current last name , and maybe Poppes as other last name (with explanation in bio).