A trainer at my gym approached me today and asked me how often I trained. I said 5 times per week, he said "wow, that's a lot". I wonder why, since I consider 3 low volume strength sessions and two medium length interval sessions to be normal for someone who has an average level of physical fitness. How many times really means nothing. What you do is what matters most.
It's hard to say how often one should train, because outside the physiological adaptations, we have many neurological and psychological factors that come into play. I jokingly say that the amount of training is judged very much like the amount of wine you can have, you know when you've had enough to feel good and when you've had too much, because inevitably, you'll have a symptom pointing you in the right direction.
If you are the average person who works out to look and feel better and maybe lose a couple of pounds, you can work out as little as twice per week. Three times per week is excellent, if you work your whole body each time. As soon as you reach 4 strength training sessions, you would have to choose to focus on lower or upper body or choose between different movement patterns, since you would be overworking your whole body if you trained it each of those 4 times.
If you are looking to lose extra fat, doing your energy system training, including body weight circuits, complexes and intervals, can be done on two or three extra days separate from your strength training days.
With women, training should be very well dosed, since oftentimes we tend to do too much, then have raging appetites in answer to the hard efforts in the gym, which ultimately sabotages our fat loss goals. Shorter duration (<45 min) workouts, heavier supersets of compound movements and short aerobic workouts work best in combination with a sound calorie reduced diet.
Frequency should be recorded together with the other variables in your workouts: exercise type, sets, reps, tempo and energy level before and after workouts. Since overtraining is reserved for more serious athletes, the best way to know you have overtaxed your system is lack of desire to train, looking for excuses to avoid the gym and loss of general strength. If you choose appropriate and challenging exercises that you switch around every few weeks you should be able to gain strength in most of them, if not, you may be doing too much or resting too little.
I've had my own coach for a while now and one thing I noticed is that we do less volume and less frequency than I ever did before, yet it's so much easier to stick to a diet and get good and lasting results, both in functionality and strength and body composition.