She might be thinking of future generations.
Who would take care of the old? Do we have the right to live forever and deny potential offspring?
New children means new experiences... means new ideology... means they have the power to change the world. If everyone lives forever, or for an extended period of time, then things just... stay static.
You would not get old if you lived 1000+ years. Then a 300 year old person would look the same as a 30 year old today. That person would probably retire at middle age of 500 years with all the money or some form of credit saved. The right to live applies for everyone and takes precedence over offspring. Not many people would be willing to suicide just to "get out of the way" to make room for children. As for new ideas, you can teach an old dog new tricks.