There are a couple of ways which you could wrangle the narrative to produce this argument, but on the whole they lapse into counter-factual history. Agincourt was a decisive battle in the Anglo-French conflict and the following period of warfare combined with Dauphin Charles's participation in the 1419 assassination of John the Fearless, duke of Burgundy, put him in a very tenuous position after the Treaty of Troyes which excluded him from the inheritance made Henry V heir to Charles VI, and formed an alliance between the new duke of Burgundy, Philip the Good. Combined with the many defeats Charles suffered up to 1428 he was rather desperate and had this not been the case then it is unlikely, but not impossible as Charles did have a penchant for mystics, for Joan to have risen to such prominence.

The problem with the argument is that it implies a historical determinism from Agincourt onwards. If Dauphin Charles had not been implicated in the murder of John or (a very unlikely scenario) patched up relations between the Armagnac and Burgundian factions there might never have been a Treaty of Troyes, or if Charles VI had survived more than a couple of months beyond Henry V there might not have been as much emphasis on crowning Dauphin Charles, or if Dauphin Charles had been more successful in his battles against Duke Bedford in the 1420s there mightn't have been a need for Joan. If Henry VI had died in his infancy the English claim would have been much weakened but Bedford, uncle of Henry, might have been more successful in prosecuting the war or England might have fallen into civil war.

Counter-factual history can be a useful tool, but attempting to create a significant point from which all later history stems is anathema to good methodology. As it stands Agincourt was but one of many factors contributing to Joan's sudden and unlikely, but not wholly inexplicable, rise in Charles's court.