I won't write up a program for you - you really should be writing in the weight training section for specific advice on a program. But...
1) A good program should include deep knee bends (squatting movements), hinges (deadlift-style movements, bridges, hyperextensions etc), upper body pushes (bench press, push ups, dips, overhead press, etc) and upper body pulls (pull ups, lat pull downs, rows, upright rows). And it should include a relatively even amount of these movements (so, for every upper body exercise, do 1 lower body exercise; for every squat do a hinge; for every push do a pull). It should have you starting below your limits focusing on form, and progressively adding to the workload as often as posible without sacrificing good technique - in fact you should aim to continue improving technique as you go. It should include a sensible warm up for each movement, and it should focus on making you stronger than you are now.
2) You could alternate between a resistance training circuit and a pure strength session every time you train. Wouldn't be a bad way to go. So long as you have at least 1-2 pure strength sessions per week, you'll do alright. You might do an A/B split where on day A you do max strength training and on day B you do a resistance-based circuit, training 3 non-consecutive days per week and alternating between day A and B every time you walk in the gym.
3) Your age doesn't directly affect what your program should look like, nor does your sex. You might have some limitations or special requirements that have come with the last 30 years of your adult lifestyle, for example people who've spent the last decade sitting at a computer often have muscle imbalances and postural issues caused by it, but being 48 and female, in and of itself, is not an issue that really needs addressing in your program.