For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
Was she an apostle, yes! If you use the word apostle correctly. An apostle is not just the 12 who Christ chose. Obviously, since Paul became an apostle years after Christ. What is an apostle? One who was taught directly from Jesus. When the 11 remaining apostles needed to replace Judas, they had to pick among those who were with them when Christ was alive. As Paul said, the two ladies were in Christ before he was, so very likely they came into Christ while Jesus was still alive. Paul became an apostle when he met Jesus on the road to Damascus.