Ranting and Raving

I noticed something in the torah reading yesterday in the passage about the ben sorer u'moreh, the stubborn and rebellious son:

If a man have a stubborn and rebellious son, that will not hearken to the voice of his father, [or? and?] the voice of his mother, and though they chasten him, will not hearken unto them; then shall his father and his mother lay hold on him, and bring him out unto the elders of his city, and unto the gate of his place; and they shall say unto the elders of his city: 'This our son is stubborn and rebellious, he doth not hearken to our voice; he is a glutton, and a drunkard.' And all the men of his city shall stone him with stones, that he die; so shalt thou put away the evil from the midst of thee; and all Israel shall hear, and fear. (D'varim 21:18-21, JPS translation, bracketed text mine)

(Spoiler alert: it never happened.)

I know from previous study that the rabbis placed so many restrictions on this that it couldn't actually happen. The son has to be old enough to be culpable but still a "son" and not a "man", which they narrowed down to a span of three months. The parents both have to be present and capable in various ways (for example, able to walk and hold onto him, able to speak, etc), and if either parent bails, it's over. Because it says "our voice", not "our voice*s*", their voices need to sound as one. There's more (mishna in Sanhedrin chapter 8 is a good place to start), but you get the idea -- lots of restrictions making it very unlikely that it could be carried out, and some key sources say it never happened at all.

The thing that struck me this past Shabbat: they didn't disqualify the mother as a witness. Pretty much everything judicial requires two witnesses, the parents are the only witnesses described by the torah, and in other matters the rabbis are clear that "witnesses" means "adult men". Yet here, rather than say that there aren't two valid witnesses for the son's transgressions, the torah says to proceed to a capital case.

So can women be witnesses or can't they? If not, they why here?