Welcome to rootschat inertia (great name).

A few thoughts/ideas:
Are there any other family who might remember her birthday?
Obviously if you have her marriage and she gives an age at marriage, you will have an idea which year she was born.
Can you give us some idea of time frames?
Do you know the names of her parents? You can try searching for all children with father痴 surname and mother痴 surname if you enter the details here:
https://www.freebmd.org.uk/cgi/search.plIf she is deceased and you would like some help, post all the details you know about her and we will try to help.
Without knowing some dates, it is difficult to advise where else to look.