I am guessing that those ladies are insisting on the children’s RCIA course because “that’s how it’s always been done” or because they honestly don’t know any other way for your daughter to do it. If the children’s RCIA class is too young for your daughter, by all means inquire about the adult RCIA class. Would the intellectual level or vocabulary level be above her head? At some point the adults may want to discuss questions of a sexual nature (all those hot button issues facing the church today), for example, and shouldn’t do so in front of a 12-year-old. Maybe they could schedule that discussion for one night when your daughter will be asked not to attend? Or maybe if they’re willing to keep the discussion delicate, maybe your daughter could attend with you there to chaperone? Maybe you could attend every class to explain things further to your daughter that she’s too shy to ask about in class? You need to judge your daughter’s readiness for that.
But if that option doesn’t work out, perhaps you have the option of homeschooling your daughter’s sacramental preparation. Your parish may never have done so, but that doesn’t mean it couldn’t work out. I get all my Catholic educational materials from
www.setonbooks.com. I like that they’re solid catechetical materials, not touchy-feely fluff with no substance. No talking clouds or stars there!

But they do have reproductions of beautiful, inspiring, great works of classic Catholic art. Browse under their religion section and see if you and your pastor or DRE can agree on a course of study. If you homeschool, you can proceed at your daughter’s level and pace.
Because I homeschool my children, I have asked to homeschool them for their sacramental preparation also. At our last parish with my first child, I wrote a letter to the pastor and director of religious education, and they had no problem with it. They didn’t even look at our textbooks, and I attended evening parents’ meetings and my daughter attended a Saturday morning half-day retreat. At our new parish with my second child, the pastor and DRE were more leery of my request. They did ask to inspect our textbooks before giving permission, the DRE “tested” my daughter with a 30 minute discussion to check her readiness, and I and my daughter did everything else (parents meetings, rehearsals) that other parents/kids (CCD or Catholic school families) did.
Definitely work on finding something that engages your daughter, don’t let her suffer boredom through activities planned for eight-year-olds. That kind of turn-off will affect how she feels about the Faith.