What is the ruling on attending mixed family visits if the girl is unable to separate men from women, and her parents or the visiting party do not agree to the separation?

The fundamental principle is that families should not mix in their gatherings if there are non-mahrams present. Men should have a separate gathering and women should have a separate gathering, as this helps avoid temptation (fitna). However, if a gathering occurs that is free from suspicion, and the Islamic legal guidelines are observed, such as avoiding seclusion (khalwa), women maintaining their hijab, and refraining from speaking in a soft or alluring manner, then there is no harm in it.