This is not true, female has estrogen hormone which produces adipose tissues that stores fat. Due to this hormone, females tend to be softer than their male counterparts as they lack some amount of muscles and are easily prone to joint injuries. Therefore, it is very important to add weight training for women to help them build muscles and further tone their body. This also prevents joint injuries, provides them proper shape and strength. Muscles development also helps to increase basal metabolic rate which in turns aids digestions and reduces fats considerably. As a matter of fact, females are not prone to develop muscles easily as compared to males. This is because the level of testosterone which helps in muscle development is less in female and thus they are less likely to develop that big and quality muscles even though they lift more heavier weight than males.
Conclusively, A normal working women or even fitness coach or consultant can increase their strength and stamina by doing weight training without appearing muscular.