Believe it or not, this is a very easy question. Divide your estate 50/50 between your two children and then forget about it. Ignore your daughter’s comments completely. When you speak to your daughter you think you are talking to an intelligent, highly educated, mature person, which 99% of the time is true. However, in this one situation, you’re not. As regards her relationship with you and her brother, you are talking to a thirteen-year-old child occupying a 38-year-old body. Catherine has always had the hidden belief that you preferred the baby of the family, Bryan, over her. Why do you think she got straight A’s and went to medical school if not to win your approval? If you leave her a lesser share, you will confirm that belief forever that Bryan is more special than she. There is a part of her that will forever think that if you really loved her, you would signify that love within your final written document of this Earth by giving as much to her as you give to her brother. Do not alter that plan.
Remember if she sincerely wants to benefit Bryan with her share of your estate this can be accomplished both before and after distribution. There is nothing stopping her from helping her brother. Just let it be her decision, not yours. One more item: do not make it indirectly your decision by telling her that you are doing a 50/50 split but it would be nice if she helped her brother. Just write the Will and let Catherine figure it out, or not, on her own.