I thought a little about this question and I have an observation that hasn't been mentioned. One of the chief reason, if not the only reason for mentioning who went to the tomb is to provide evidence of the risen Christ. Christ's own mother may not be the best witness to site as proof of the event. Further, I wondered if Jewish law which is fairly specific about number of witness, can't testify for self etc, have anything to say about mother or father as witness. Just curious.
A fresh point of view, I'll have to think about it (I have to go now...)
The witnesses are another point. Do they need two? I can't remember, but do they have to be men?