She was indeed conceived without sin. That’s how God saved her. She didn’t “pull that off” herself.
Chapter and verse, please?
At best we have a picky point here that seems to destroy all charity and grace in taking umbrage over it. She would have been a participant in sin prior to her own conception in the fall of mankind, if that were so.
In which case Mary needing the work of the Cross still stands as a fact. The Cross operates spanning all time and space. But it was to appear in Mary’s earthly time line as well as in Mary’s pre-conception past.
This is being all hypothetical about it. As a rascally Protestant I say this is special pleading and not needed to be a foundation of anything that Christendom (certainly the bible) validly honors.
If something could be counted on to put a Grinch in Christmas, these kinds of arguments are it.
Of which there is no biblical support for your assertion.