What is the correct action to take regarding intrusive thoughts of gas that appear intensely when intending to pray, knowing that the questioner does not suffer from chronic flatulence, and that this condition has affected her performance of supererogatory prayers?

If the sensation of gas is merely a delusion, then one should disregard it and pay it no mind, proceeding with purity and prayer. However, if there is a firm certainty of gas discharge, and it does not stop for a sufficient time to perform ablution and prayer, then your ruling is that of one afflicted with سلس (incontinence). So perform ablution and pray, and what comes out will not harm you, while also consulting doctors.