It appears that the rose has a virus called rose rosette.  Witches brooms are only one symptom of this fatal disease.  Roses with rose rosette exhibit:
Red leaves and possibly twigs
Leaves are distorted and twisted
Excessive leaves
Possibly excessive or large thorns
Ends of branches may have witches brooms

This is a virus belonging to a new group of Emaraviruses.  It is transmitted by tiny Eriophyid mites. Roses decline and die but are also capable of passing it to other roses.  This is not a fixable problem.  The best idea is to destroy the plant, especially if you have other roses that are unaffected.

Oklahoma State University has done a great deal of research on rose rosette.  If you look online, look for information from them.