While your argument is convincing, there is some prior evidence against it.

For example, given Egwene's strength (she's at full potential), there is simply no way Silviana can hold her shield, yet she does in the prologue of KoD. Amys mentions the difficulty of holding Egwene, and by Egwene's own estimation, Amys is stronger than Silviana or equal to her.

The only difference between Amys' shield and Silviana's is that it is entirely possible Barasine and Katerine linked to shield Egwene, and Silviana could still hold Egwene because she merely assumed the shield.

Should this be the case, it could be that a moderately strong Aes Sedai could indeed hold Semirhage, as long as the initial shield was woven by more than three women (am I right on the minimum here?).

Also, could it be that Cadsuane meant that if she left woman alone with an angreal, the woman can hold Semirhage, but the angreal was just not mentioned? That would certainly work, and be a minor mistake.