I have some strategies that I find helpful when dealing with a daughter or student who isn't giving me her best.
The first thing I always do is find out what she is truly capable of. Is her struggle due to an actual lack of understanding or is she just trying to get out of the work? Is she not understanding some of the terminology or is she only completing the first step and not wanting to do the rest? It's all about knowing the kid you're dealing with.
After that, it's addressing the issue. If she doesn't understand, reteach the skill. If the vocabulary is tripping her up, rephrase. If she just doesn't want to work, motivate her. I have found the best way to motivate those students (and daughters) is by finding inconvenient times to offer help. Not inconvenient to you. Inconvenient to them.
All three of my girls would lament, "I just don't understand." And when asked what they specifically didn't understand, their answer was, "All of it." So after determining they were actually capable of doing the work, I came up with a plan.
Let's take for example Amy's complete dislike for elapsed time problems. For a fourth grader those problems represent multiple steps. Amy prefers questions that can be answered quickly and with only one step and little critical thinking (don't we all). One day she had two elapsed time problems on her math assignment. She took two wild guesses and moved on. I marked them wrong and gave them back. This wasn't a new skill, rather one she just didn't like. After two more rounds of guessing I let her move on, telling her I would find time to help her later in the day.
Later came. Unfortunately it came just as the other girls were heading outside to play volleyball. Amy and I worked through the elapsed time problems together. She knew she not only could have completed them correctly on her own, but could have done them much quicker than when I was helping. It's all about motivation.
As teachers it's hard to not want to help that student who tells us their struggling, but it's also our job to wean them off of our help and let them do their own work. It's a fine line. And not one that I'm always successful at determining.
As a final note, just know that when I just can't determine a student's actual ability, I always err on the side of dependence. I'd rather over-help than under-help, if you know what I mean.