I've only had one go through the ERs so far (second is now in the Bible), but we didn't need to use any of the supplemental titles. By the time we finally got done the Bible (it seemed long, since there are so many stories, but he needed the practice), he didn't struggle with any of them, and ended up skipping the last 3 books because he wanted to read Stone Fox (DITHOR Level 2) so badly, that I let him, and he just kept moving on from there.
If they struggled, I would have (as my DD likely would have, if we'd been with HOD when she was that age).
As for pacing, if she is reading really easily and fluently, with expression, then you could do more than one day's scheduled assignment each day. But be careful not to allow the reading time to take too long, for her to get tired or frustrated. Once she starts to need to sound out more than a couple of words on a page, or she's stumbling, not able to answer questions/her comprehension becomes less, etc. (any sign that it's becoming more of a challenge) then I suggest slowing back down to only one assignment per day, even if that only takes 5 minutes. You could, of course, go back and get any of the past supplemental titles, ones that are slightly easy, if she wants to do more reading, but is finding her current ER level to be "instructional" (3+ words/page are new, it's slightly challenging, etc.).
Blessings,