When is assisted reproduction (such as ivf) a good option for a woman?

Depends. It depends on the causes of infertility and how soon you desire to achieve pregnancy. For example, if you have severe male factor infertility or tubal factor infertility, you may need ivf right away. But if you have ovulation dysfunction or endometriosis, you may try medical or surgical treatment first, if after 3-6 months try, you still not pregnant, you may need ivf. It also depends on your age.
When you are ready. Ivf offers the best chance of conception for most couples with fertility problems. In general pregnancy rates are 5-10 times the natural conception rate. In addition, ivf offers ways to limit multiple pregnancy and to reduce the risk of genetic illness in pregnancy. The main barrier is cost. When easier and simpler methods exist, they are usually tried first.