Kim,
Lynn did a good job of helping you talk through some possible options. Often talking with others helps so much in figuring out a plan for moving forward.
One thing I will share is that typically we would almost never advise for a 6th grader who is new to HOD to begin in Rev2Rev. Age 11 is the very youngest age at which Rev2Rev should ever be used (and this would typically only be for a child who has come up through HOD's previous guides). This is because it takes an incredibly strong reader, writer, thinker, and independent worker to thrive in Rev2Rev as a 6th grader. The guide is also assuming that the child has a strong founding in CM style skills and that the child has honed these skills with a parent's help in previous years.
With this in mind, and the things that you have shared about your 6th grader thus far in the thread, I would lean toward placing your 6th grader in CTC instead. This is guide in which the child is gaining some independence, yet has many of the helps needed in the guide for him/her. The assignments and readings are shorter and the directions are less lengthy. It has the stepping stones toward success in a RTR and Rev2Rev that your child will need to succeed along the way.
While you could drop things from Rev2Rev to make it easier, or pull the guide back to a slower speed, I fear that in the long run your child will always then be unprepared for the level of rigor in each of the guides which come later. You will then be in a continual pattern of dropping, adjusting, and rewriting the plans, which will take away all of the beauty of the open-and-go feature our guides are intended to provide.
Keeping yor 6th grader in Rev2Rev will mean that she would be in grade 7 doing MTMM and then in grade 8 doing our first high school guide. Some kiddos who have come up through HOD may be able to do this, but most kiddos would find doing a high school guide in grade 8 to be overwhelming!
The good news is that if you make the adjustment now, your child will be better prepared for each guide along the path.

I am not saying that changing guides will make your child's school day suddenly easy or have her completely loving her day immediately, but you will know that she is better placed and will be better able to help her without having to continually downsize.
A CM-style education takes some time to get used to and has many new skills. It requires a different type of slower, more thoughtful reading which means that there is an adjustment period when switching from fact-filled, full-color picture style texts to more living readings (where the words paint the pictures instead of the photographs doing that job).

The connections among events and people that come with a higher level of reading material can take time to develop. This is likely what is mostly missing from your 6th grader's reading experience in Rev2Rev. If she is not seeing the connections between people and events all over the world as she reads, often in frustration this can result in something being called "boring". This is a complaint that is a catch-all for so many issues, such as frustration, being overwhelmed, feeling something is too difficult to understand, not being colorful enough, requiring too much work to read, not having enough knowledge to make the connections come alive, not being able to discern what the text is saying, or simply hoping the assignment will then be adjusted or removed etc.
I'd love to hear what you think. If you get a chance to pop back and share that would great!
Blessings,
Carrie