The healthy weight for a 42 year old woman that is 5'8" is 126-167 pounds, depending on her body frame. This number doesn't take muscle mass into consideration.  Portion control and eating healthy foods plays a huge part in that as well.  Foods high in protein, low in carbohydrates (skip the pasta, bread and potatoes) and low in refined sugars are what you should be looking for to help with weight reduction.  The two huge things that helped me with the portion control are to NEVER put food on the table.  Put your food on your plate and take the plate to the table but not having the food there in bowls or pans prevents you from taking out more.  The other thing is change the size of your plate.  So many of us are used to eating off of large dinner plates.  Most dish sets come with either salad plates or what used to be considered "saucers."  Start using the smaller plate.  You will get used to portion control much easier when you reduce your plate size.

I used to eat off the dinner plate.  Now I use the salad plate.