Are there halachic concerns for a woman to daven in a shul that does not have a mechitza?

Shalom, Thank you for your question. A mechitza that separates between men and women during prayer in a synagogue is a basic part of religious service. All Orthodox synagogues have such a mechitza – whether it be in the form of a balcony, a curtain, a partition or even separate rooms. These laws are learnt out, in part, from the separation that existed in the Temple between men and women, during the Succot festivities. In the middle of the 20th century the issue of the mechitza became a “hot topic” as the Conservative movement departed from the traditional synagogue mechitza. At that point, many Rabbis addressed the topic, and it became a defining feature of all Orthodox synagogues. Some great Rabbis understood, that at that point, as the mechitza was now more than a halachic obligation to separate men and women during prayer, it now had the added issue as a definitional issue, and as such was even more obligatory. In any event, the short answer to your question is that there are certainly halachic concerns for a woman to pray in a shul that does not have a mechitza – just as there are for men. As to the question if these concerns can ever be put aside in certain cases; there does exist certain situations that would allow praying in a shul with no mechitza (by sitting separately from the men) – but this would only be in special cases, that would have to be addressed on a case by case basis. Blessings.