She's overstepping. I agree, have your individual bid day/welcome home celebrations as each chapter sees fit. As long as there aren't boys, booze, etc. involved, I don't see how or why she feels these can't happen in the winter. Informally recruited new members deserve a warm welcoming event. She doesn't need to be involved at all.
I was an "open rush" pledge and there was no "bid day" in the spring or fall for open rush pledges. You got your bid individually, not all at once.
But at a chapter I worked with, fall formal recruitment had not been a huge success and lots of chapters needed to pledge that spring. So they had a sort of formal/informal, complete with rounds and a bid day, but much much lower key. I thought it was lovely. I always regretted not having that exciting day.
Why not? Who's it going to hurt?