Mechitza for Prayer (1)

Sometimes a quick exchange communicates more effectively, and more personally, than an article. Sometimes, just seeing that others share our questions can make us feel more connected. Our posted questions and answers are an opportunity to learn from each other. Keep in mind that each questioner’s situation may be unique, in ways that affect the halachah. Even the tone of a question can affect the tone of an answer.
Hi! Until what age can girls daven with their fathers in the men's section? Are there any Halachic sources on this? Is there room for leniency until Bat Mitzvah?