Not only is it acceptable to freeze eggs before beginning treatment so that she and her husband will still be able to have children later, but it is proper to do so (and would be the same if the question were a man wanting to freeze sperm before beginning treatment that could cause sterility, since it is being done for the sake of procreating).
It is a great mitzvah to have children, and doing this will enable her to still have healthy children down the line. Furthermore, I love the way this shows a sense of confidence and affirmation of life in the face of serious health challenges and dangerous treatments.
My deepest blessings for a speedy recovery and a happy, healthy family in the future.
If this question is not just hypothetical, I wish a refuah sheleimah, a complete healing to the person the questioner is writing about.
As a rabbi, it is always nice to get a question which can be answered with an unequivocal YES.
One might follow-up with questions about IVF or other assistive reproductive techniques which would be required to turn those frozen eggs (or embryos-depending on methodology) into healthy children. The answer to those questions would also be yes! As Jews, we strongly support the creation of new life and new Jewish babies. The Conservative Movement even has a rabbinic paper encouraging families to have more children than they might otherwise consider. (http://www.rabbinicalassembly.org/sites/default/files/public/halakhah/teshuvot/20052010/mitzvah_children.pdf)
I wish you much success with treatment, recovery and family-building--all in their proper time and place. I pray that you and your family will have the strength and patience to journey successfully through this challenging time. Know that their is a light at the end of the tunnel and I commend you for thinking about your future, even when one might be afraid to imagine that far ahead!
Thank you for the opportunity to answer this sensitive and personal question.
The answer is a simple yes. We recognize that modern technologies have allowed for the possibility of freezing eggs. This can be done for many reasons. But freezing them in order to allows future pregnancies or surrogacies from those eggs is permissible by Jewish law.
I wish I had more to say on the topic, but it is relatively straight-forward. If a member of my congregation were in such a situation, and they felt this was an important option, I would strongly support this.
We live in a world of amazing possibility – and the option of freezing the eggs of a woman struggling with cancer for the benefit of future births - is an opportunity to open the door of a mitzvah when it might have otherwise been closed.