Hi. This issue is something that your friend should discuss with his/her Orthodontist who is treating her. No two people are the same and we can not generalize the treatment protocol to the minutest detail. We have to treat every case differently. It also depends on what your friend is expecting our of the treatment. Only the treating doctor will be able to explain why only the upper braces are required and not the lower ones. In general, if you ask whether it can be done or not, i would say yes. It can be done depending on the expectations of the person getting treated and on the condition of teeth.