Only one eye? ??? If it was the cayenne pepper, it would seem like it would be both eyes. Also, this is the first bloodshot eye I've heard of in about 600 postings. It could be something unrelated to the cleanse, like she rubbed her eye or got something in it.
More likely she is just having a detox symptom. Has she ever had this happen before? After all, this is her day 3. In my book, Lose Weight, Have more Energy & Be Happier in 10 Days, I point out that days 2, 3 and 7 are the worst.
I'd recommend she not change anything for a day and see if it's gone or much better tomorrow. That would be the result if if's just a detox symptom. If it's not better, then I would suspect it's something else and recommend she consult a licensed health care practitioiner.