There is absolutely no problem ingesting magnesium with ascorbic acid. Magnesium ascorbate is actually produced that way, i.e. mixing the two together. However, if it were me, I would see what a Bowel Tolerance daily dose of ascorbic acid alone could do for my health [assuming a daily healthful, i.e. minimally acceptable, ingestion of magnesium in/with the diet and or supplementation], because, while there is no known upper-limit health risk with ascorbic acid ingestion, I am fairly certain that is not the case with magnesium.
I hope that helps, Jeanne, and best wishes,
JFYI, I have ingested a Bowel Tolerance dose of ascorbic acid [via one gram tablets], in HEALTH, not illness [of which I have had virtually none], basically every day since 1994, amounting to [currently], on average, 75+ grams [daily], in 10 to 15 divided doses.