All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and messenger.
The presence of a Mahram is a condition for a woman when she is travelling but it is not a condition when she is a resident of a settled population. Therefore, if she is a resident in a safe place, then this is permissible. For more benefit, please refer to Fataawa 88977 and 155371.
We do not know the reason for which the Islamic Center stipulates this condition. It might be that there are some circumstances which led them to stipulate such a condition.
As a basic rule, seeking knowledge should be facilitated for whoever wishes to do so, and all obstacles which might hinder the achievement of such a purpose should be eliminated.
Anyway, if you are not able to join any Islamic Center, then the means of acquiring knowledge are easy in this day and age because of the technical advancements achieved with the information revolution. So you should use these means and Allaah will facilitate for you this matter. If you are sincere, then Allaah will surely help you. Allaah says (what means): {And when the matter [of fighting] was determined, if they had been true to Allaah, it would have been better for them.} [Quran 47:22]
Allaah Knows best.