I think this is a situation where letting the teacher know that she tried and struggled with something is the way to go. The teacher won't know what the students didn't understand and what she needs to go over again unless the students come in and say "wow I was totally lost on homework last night." Also, middle school is a time when many teachers stay after school for an hour to give extra help to anyone who needs it. She should see if her teacher has office hours after school and avail herself of the opportunity to get the extra help that she needs from the teacher.

The thing with math at this age is that teaching order and teaching methods vary widely from curriculum to curriculum. I teach SAT prep part time. Math was never my strength but I know pre-algebra, algebra I, geometry and the half of algebra II cold. Yet I was not a good fit for helping my SD when she switched schools in 7th grade and had to catch up to a more advanced curriculum. I would teach her how to do a problem the way I knew how to do it (which would yield the right answer) but it wasn't the 7th grade methodology that she was learning in class, so I heard lots of "that's not how we do it in school" and "that can't be right." So she learned to stay after school and do her homework with the teacher right there to answer any question she had.

Our local library has an subscription to a free on-line tutoring program. I don't know the name of it, but check around to see if there's a similar resource in your area. That might be a good resource for when she's not completely lost, but just needs help getting through one step.

The general rule to remember, if she is in pre-algebra or a precursor to that, is that if she needs to solve for a variable, you just do the same thing to both sides until the variable is alone. That may not apply to what she's working on, but I remember having to repeat that to both of my oldest kids and take them through how to do that step by step again and again.