I feel like telling a woman she has "plenty of time" in her thirties is irresponsible. It sucks, but women don't have nearly as much leeway, or the luxury, to put off having children like men can. It's something of a toxic myth to let women think can put off children until their 30's or even 40's - it can happen, but it's so much less likely to happen than if she was in her twenties. The woman who had a child at 47 is an oddity, not a standard to be compared to.
Personally I think schools should hammer home that women should think about these things earlier, just so we can be confident women doesn't miss the boat from lack of urgency. Too many women now are missing their chance, which is only fuelling the declining birth rates world wide; not to mention how tragic it is for a woman to miss out on having a family simply through poor timing.
Of course, this is all irrelevant to the story, as the doctor was just encouraging her by saying those things, but the author is spreading the terrible advice in this comic.
(This isn't to say men can just put off having children either, there's reasonable evidence to suggest that the growth in things such as autism is caused by men having children later. However, if women wanted to have children earlier, men would likely naturally follow.)