Have worked with many clients 50 and older, one thing I would avoid at the outset is getting comfortable referring to this population as “older,” lest you do it in their presence! I’m mentioning this because you used the description twice in your brief question, although I do recognize you may not be using it at all with her.
I also recognize the scientific literature and mainstream media often refers to this age group as “older,” but I can assure you most of them do not think of themselves this way and don’t appreciate the reference. I received a great tip from a client recently who said he prefers to hear the information in the context of his specific age group, rather than with a label attached – for example, saying “when people are in their 50s, it’s a good idea to pay attention to ÔÇÿx, y or z.’”
Beyond that I think others here have provided good advice. Although there are certain common physiological changes to be aware of at different ages, there is no single regimen that is appropriate for an entire age group. Each client should be assessed individually with regard to his or her health & injury history as well as baseline strength, aerobic capacity, flexibility, balance and biomechanics. You need this information and an understanding of its implications in order to proceed safely and effectively.