It may be a good idea to use a buffered or liposomal vitamin C if being used in an enema. From what I gather the acidity of a pure ascorbic acid enema would be similar to that of an ACV enema. The acidic environment it creates would kill both good and bad flora in the large intestine.
Of course, the length of time she kept the enema in would make a difference as well as the amount of fluid she used.
Even though its more expensive, it may be better to try for vit c IV if she wants to try this.