badly ailing rose

My rose Crown Princess Margareta which has always been a pride and joy and a super performer is looking utterly miserable this year, although all other roses in the garden are doing fine.  I thought it might be heat/drought stress although I watered it, maybe too much.  I have now given it a granular feed which I neglected to do at the beginning of the season, because I gave it a dose of Uncle Toms Tonic and forgot to feed as well. I  I am inclined however to cut it back, take off all the drooping buds and damaged leaves and just let it do its own thing for a few weeks.  Is this a sensible option or should I just leave well alone.  Thank you