I work with a Rheumatologist who specializes in this and is putting out a paper regarding this work. I must stress that relaxation is one key. To assess your level of relaxation, you should make yourself body conscious. Have a friend observe you playing the harp. Then consciously relax.
Placticed relaxation is important.
Secondly, you must take timed breaks, even if you are really enjoying yourself. 45 minutes has been standard. If you suffer from RSI, the breaks may have to be taken more frequently at first. If you must, use it only as a reminder that the wrist or shoulder is the problem and the brace will not fix it. I replied to this because I had received earlier inquiries on RSI and just figured out the new mail system I am using.