What's a term (one or two words) that describes someone who is calm and also has lots of energy (particularly a woman)? i.e. They are not necessarily extroverted nor do they expend a lot of energy all at once and then become exhausted. They are grounded, with a good supply of energy to get through life.
a person or thing of great energy, strength, or power.
"she appears to be an intellectual powerhouse"
If you’re willing to accept metaphors, consider marathon runner (or the one-word alternative, marathoner). A marathon is literally a running race of 42.195 kilometers1. The word is used metaphorically to refer to any long-duration activity (in contrast to a sprint). For example, Stack Exchange’s recent four-year effort to support HTTPS throughout the site easily qualifies as a marathon.
Long-distance running requires a lot of energy, to be doled out gradually over a long period of time. In other words, long-distance runners require stamina. And then there’s this:
A runner will typically have a lower pulse and blood pressure than someone who isn’t as fit because a runner’s body is able to work more efficiently, notes Lawrence Horwitz, a cardiologist and professor of medicine at the University of Colorado Health Sciences Center in Denver.
As far as I know,
there terms do not imply anything about personality or philosophy of life,
and they are not sex-specific.
1 Somewhat amusingly (to those who are amused by this kind of thing), Google’s Units Converter recognizes a “marathon” as a unit of distance, along with more traditional units such as “mile”, “foot”, “inch”, “Ångström”, “furlong”, “light-year”, and many more. So, for example, 1 typesetting (PostScript) point equals 8.36065e-9 marathons.