Ellen’s final secretary from 1902–1915, D. E. Robinson, even stated that he was present at camp meetings with Ellen White where she would pray standing.
The Bible nowhere says kneeling is required to pray (Mark 11:25). And while it may seem like making a big deal out of nothing, Ellen White claimed to never write one sentence of heresy, that the words in her books are barricaded by a “thus saith the Lord”, and that she doesn’t write merely her own opinion, but what God has revealed to her. She set up the standard for herself that it’s either all of God or all of Satan and that “whatever contradicts God’s Word, we can be sure proceeds from Satan.”
Someone making such grandiose statements earns being critically examined. Did God really reveal to Ellen White that prayer was to always be done kneeling to only turn around and say that isn’t the case? Especially after Jesus himself said prayer can be done standing?