Do some research on the topic, it may change your mind. Or not. I don't care.
Timing is everything.
I have a lot of experience with IVF and can tell you the timing is not always as easy as an article on the topic makes it seem.
First off, the timing of obtaining a genetically normal embryo to implant can vary drastically from one person to the next. You have to medically induce multiple eggs to mature to the perfect stage, harvest those eggs without damage, get sperm to impregnate the egg in a Petri dish, and then see which embryos are genetically normal. Some women only need one round, but it is not uncommon for women on the older end of the spectrum to need multiple rounds of egg retrieval before they even obtain a single genetically normal embryo that is feasible to implant.
Since most older women are having their embryos genetically tested prior to implantation, this involves harvesting a few cells off of a very small embryo and sending them to a lab for genetic analysis. This process of removing a few cells to genetically analyze can potentially damage the embryo to the point it is no longer viable and the cells will no longer continue to divide. When will you know if this is the case or not? Only after you implant the embryo and see if it actually sticks into the uterine wall and continues to develop. Many women may only have one or two genetically normal embryos and if they do not implant as intended, then the process starts all over again. The entire time the biological clock is ticking.
So while you do have some say in timing, any good reproductive endocrinologist doing IVF will advise their patients that ‘sooner is better’ when it comes to the IVF process. This becomes more and more true as the mother advances in age. The clinical outcome data can differ pretty significantly from a 39 year old woman to a 40 year old woman.
And lastly, the vast majority of couples seeking IVF are DESPERATE to become pregnant. They have often endured multiple lost pregnancies and that begins to weigh heavily on a persons mental state. When you have the chance, you jump at it regardless of timing and regardless of cost. She made the right decision.