I view it in much the same way as I would if I, as a parent, do not speak English, and no English is spoken in our home (hypothetically). However, (hypothetically), we have moved from, say, Finland, to the US and have enrolled our children in public school. So, if our children come home with an assignment, I, being only able to speak Finnish, cannot give any assistance. I can make sure our home is one in which learning is appreciated, where there is time and space for homework, but that's not the same as helping with homework. It doesn't matter if it's math or history or anything else. The same would apply if I were illiterate, but had determined that my children would learn to read and write, so I make the valiant attempt to send them to school, even though I am unable to read a simple menu in a restaurant.
So, in those cases, it's up to the teacher to teach the child, arrange for extra instruction, and provide whatever the child needs. The Finnish-speaking parent or the illiterate parent would not be expected to provide homework assistance.
You're not the teacher. You're expected to instill in your child certain qualities (cooperation, politeness, obeying school rules) and hopefully you instill others (willingness to learn, helpfulness, kindness, eagerness, etc). But you're not expected to master the curriculum.
What you can do is to insist on a meeting with the teacher - but NOT to get the curriculum or teaching materials. You can tell the teacher that you encourage your child, that you provide a nice place to do homework, that learning is respected in your home, but you cannot and will not go back and take a math course. Ask the teacher direct questions. Don't just tell the teacher that you're frustrated. Ask the teacher "how can you help my little girl do her homework without tears?" "What resources are there for a child who is so frustrated?" "How can you help her master the math requirements so that she is capable in math, and so that she continues to learn?" I would not request learning material or teacher handbooks. That's not your responsibility. What you need to do is communicate with the teacher about how your child is struggling. Of course the teacher appreciates a helpful, involved parent, but being helpful and involved and supportive DOES NOT mean mastering the curriculum. That's the teacher's job. Your job is to communicate effectively, and help your child speak up, to advocate for herself, to ask for help, or to tell the teacher that she does not understand what has been presented.
If the teacher just explains it the same way over and over, or tries to teach you, or scolds or humiliates your child, take your complaints to a higher level. A good teacher doesn't need fancy equipment, or a huge budget (although a better budget and higher pay would certainly be helpful) to get through to a child. A good teacher uses the available resources and figures out how to create a learner who loves learning.