I doubt it will make much difference either 2 weeks sooner or 2 weeks later. The key is often the side effects (urgency, burning/irritatation etc) become cumulative. If they become unbearable the dosage is sometimes cut by 1/2, 1/3, 1/4 even 1/10 and still get a response. To top that off there are many protocols on what regimen is the best. It does sound like your Mom is getting one of the most common ones. Pat yourself on the back. Your part of the "team" is very important. Plus, I would do exactly what you all have decided....go and enjoy life and the trip. Keep asking as you have more questions.
