Both true. Most women (and men) don't train hard enough and that's why they never see the results that they want. You should go until failure but obviously only when you can fail the exercise safely. Also, quality over quantity, form is very important. And you need to do cardio to, not just because it's good for your cardiovascular system but because if done correctly and regularly, about 150 minutes of moderate intensity a week, and paired with good nutrition, your body fat percentage will get lower, showing more of your muscles. Strength training helps with that too since the more muscle mass you have, the more calories you burn. You don't even need to use any weights for progressive overload but doing the same exercises that you started with over and over with the same amount of sets and reps won't do it. Also, if you're interested in working with more resistance but don't go to the gym or have the money for weights, use resistance bands instead, but be sure to get a set so that you can increase your resistance over time and get loop bands, and not the mini ones for your butt but the big ones, they have better resistance and you can use them for a lot more exercises.

I love how she constantly works out to maintain her figure.
She has a great body!