A few things:
Has she been tested for a learning disability? If not, you may want to talk to her about this. I can't imagine that her school hasn't done this, given what you say her reading level is, but maybe it's been overlooked if she's passing in other areas. Sometimes finding out that there is an LD at work can offer relief. It's not the FAULT of the person struggling to read that the process is so difficult.
The behavioral stuff such as not caring, being resistant, (frustrated parent) are extremely common when a child has unmet learning needs. It's a really difficult cycle. It's pretty normal for kids to feel this way, and at your stepdaughter's age there's a lot of history of reading "failure" to contend with.
If she eventually feels that she wants to work on her reading, you may want to find either a center or tutor familiar with LD's, and one that works with adult learners, given her age and experience.
Also, much of what's written that we contend during day to day life is written at about a 5th-6th grade level, so from a functional standpoint your dsd should be able to be ok with directions, instructions, general reading material, etc. I know this doesn't help with school, but a 6th grade reading level is certainly something to work with.