Great question, and one I think deserves attention.  It has a supposition, though, that women are portrayed as inferior in "The Lottery."  I am not sure that is completely true.  Let's take a look for ourselves, shall we?

First, I would say that two of your examples are not very good as proof.  The novel doesn't say that the girls can't collect the stones, it just says that they aren't.

"The girls stood aside, talking among themselves,"

So I don't think this offers proof that the girls are not equal.

In addition, the fact that the women were dressed in faded housecoats doesn't do it for me, either.  It gives no mention of how the men were dressed.  If they wore expensive, lavish clothes then that would contrast with the women...all we know is that the women were wearing shabby stuff.  The men very well could be in worse clothes. 

The second part of this is that the men came first.  I think you are assuming that their arrival at the town square ahead of the women symbolizes their power over them, but we don't have any real proof of that.  It could have just been a coincidence, or perhaps the men described were already in town on some farm related business.

"Bobby Martin ducked under his mother's grasping hand and ran, laughing, back to the pile of stones. His father spoke up sharply, and Bobby came quickly and took his place..."

Here we see that the child does not obey his mother but comes running when the dad calls.  This might show that women are not respected, but again, it is only once incident.  We don't see any pattern of women being ignored by children that might prove the point.

The lottery is run by a man, but the reason given is: "...[he] had time and energy to devote to civic activities." The implication is that a woman could have done it were she equally time-rich.

The "heads of families" thing gives you a bit of ammunition.  It is the male who is considered the head when it comes to drawing a slip of paper.  This clearly puts the women in a subordinate role.  But notice it is subordinate, not necessarily inferior. You could argue with me on this one, though, and that's why it's a good example for you case.

Mrs. Hutchinson also provides some ammunition.  She is portrayed as being kind of stupid.  I mean, how could you forget that today was the day for such an unusual event?

"Clean forgot what day it was...Thought my old man was out back stacking wood,...I remembered it was the twenty-seventh and came a-running."

But this quote goes against you:

"That's right. He's broke his leg, hasn't he? Who's drawing for him?"

"Me. I guess," a woman said. and Mr. Summers turned to look at her. "Wife draws for her husband."

The wife is able to draw for her husband.  If she was really inferior, she probably wouldn't be allowed to.

"Watson boy drawing this year?"

"I m drawing for my mother and me."

This one supports you.  The son, if old enough, takes the place of the mother.

The ultimate reason, though, I don't agree that women are seen as inferior is that they are perfectly acceptable as sacrifices.  They share the same risk as the men and suffer the same death.  This puts  everyone on an equal footing, in the end.

Best of luck to you.  I hope I gave you some food for thought.