Stand ran away before the marriage problems came up and also she thinks of him as her brother so that might be why she rejected him in the first place
stand ran away and his whereabouts are unknown to her at that time
And back then she her homeland had not been conquered yet so she had no need for an immediate marriage - especially not with someone who was like a brother to her.
True, after all she did mention her past life ( the future ) so she's speaking, thinking and acting similar to her past life style
Wait but if she just needs a successor couldn't she just have married stand and had kids and lived a happy life of the guy who truly loves her and continues to love her??