Dr. James Wade Logeman, DDS

It is not uncommon for the soft tissues on the inside of the mouth to get sore from new braces. In fact, it usually takes up to 7-10 days for the tissue to 'toughen' or 'callus' before they're back to feeling normal. In the meantime, we advise our patients to use the soft wax...pinch a piece off in your fingers, roll it in a ball in your fingers (which also warms and softens the wax), and then 'push' it on whatever is causing the discomfor inside your lips, cheeks, or tongue. Usually after a week it's not an issue. If the discomfort is from a long wire, or something that's sticking out and poking, it can easily be remedied by clipping the wire, or bending in the part that's protruding.
Once the tissues have gotten accustomed to having the braces on for a little while, the issue will be resolved!

Different types of tooth movement require different types of retainers. Some require fixed (non-removeable) retention long term. Severe rotations and excessive spacing are just two examples of types of tooth movement that should be held with bonded retainers for several years. Once the bone and periodontal ligaments around the roots of the teeth get reasonably stable, then a nighttime removeable retainer can usually get the job done. However, each case must be evaluated individually for type of retainer to use, and for how long.

Often times, if it's just minor tooth movement, alignment can be obtained with just a removable appliance (like a retainer with fingers springs in it). It would be impossible to be able to tell you if you're a candidate for this option, without seeing you.
A simple exam/consultation would likely be able to give you the definitive answer!

This is a question for an oral and maxillofacial surgeon.

I am an orthodontist... my guess is that it varies from patient to patient for many different reasons, such as age. Being younger, your sister will likely fully recover more quickly than an older patient.

Wishing a speedy recovery for her!!

Dr. Logeman