Thanks for your question.
There is no rulings against performing Hajj, Umra or Ziyarat for a woman accordingly to Shi'a Fiqh, the issue is only about safety. It is not clear what you mean by "a group of other Muslimahs". Do you mean an organized group?
The issue again is not Islamic ruling, but safety and the difficulty to get a visa to visit countries like Iraq and Iran. The most logical way is to find a hamla, a group specialized in caravans to visit holy places. Try to find a few local ones, inshaAllah they will explain you in details what is needed and the procedures.
They could be able to able to help out to perform Hajj and/or Umrah in some cases.
In preparation of any pilgrimage, I suggest you to read "Your Personal Guide to Hajj Umrah Ziyarat" at: