When I was 11 my mother passed away due to cancer. A few years later my dad decided to start dating -which I was okay with-. He met his current girlfriend about 6 months after he started dating and he was very happy with her and he appeared to be really happy with her. At first we got along okay, however after moving towns dad decided to do take on a long distance job in the mines (so he traveled back and forth a lot - gone about a week then back for 3ish days) and she started to ignore me or just out right yell at me for simple things (e.g asking what we were doing for dinner). When dad got home she would tell him how I haven't done anything around the house - which would get me in trouble with him.

(note: 7-4:30 at school - get home, do homework, feed dogs, dishes, tidy lounge/bathroom/bedroom ((proper clean on weekends)) do assessment, stuff like showering and eating, then bed at 9:00)

She doesn't have a job and has told me that I need to get a job in order to help support the house. Which I wouldn't mind doing except that she's expecting me to work at least 20 ours a week, which means I will have less time to study (I'm in grade 12 and taking a full OP course)

Recently it was my mums birthday and I asked dad if we could visit her grave (I haven't gone to her grave with my dad before - dad has never been) as she didn't want to be forgotten but my dads reply was "no, /dads girlfriend who i wont name/ would feel uncomfortable with that."

I'm 17 years old and therefore I will be moving out of home in the next few years to being my journey as a young adult (or I plan to anyway), but I want to know if there are any ways that I may be able to make a better relationship between my dads GF and myself, as she does make him happy.

I admire your diplomatic and charitable attitude, unusual for many teenagers with a non-parent in the house.
She does sound resentful of you, plain and simple. She can't be more than 45 herself, yet doesn't work or have kids?
She also sounds like she expected more from your dad, financially as well as being home more, and is taking it out on you.
My suggestion is to plan to leave home sooner rather than later, and to prepare for it now. I would get a weekend job to gain experience, so that you can move into full time as soon as school is done (in a month, right?), and move into a place with roommates to share expenses. Start looking at wages, rental and utility costs (shared), how much food is costing your dad now, and work out a budget.
Ask your DAD for help deciding how much of your wages to give him over the summer, while still allowing you to save for living on your own. Does he know that she expects you to contribute to the household now?

You're in a tough spot.

It sounds like you live with her, more than your dad lives with either one of you.

It was telling when you said that your dad's reason not to take you to your mother's grave was, it would upset his girlfriend, so he said no to you. That says much about how she deals with not only you, but him as well. What kind of person would not encourage such a visit- even once a year, for your sake. That is very sad.

As she is 'only' a girlfriend, she is not his fiancé, or his wife, which makes it harder for you to live with her, and accept her, as a mother figure. A role that she seems to be taking, which is inappropriate.

Your dad on the other hand, has allowed this arrangement to carry on. He is seldom home, and it doesn't look like he is providing any parenting role because of that. Did he move her in thinking it was better for you to have someone in the home, and at the same time, better for him that she is there so he could take work out of town?

It is important to keep the peace, of course, but, with your own future, on your own, about to happen in only a few short years, it is far more important that you reach those goals, so you can set your own course in life.

To add a job to your already overburdened schedule, will not help you reach your goals, nor will it make your life any easier than it is now. Try to find a way to have your dad listen to at least that one point about staying the course with your studies, and not adding a job to your schedule. If he has a computer with him, try sending him an email, outlining what you've said here about your studies, and your lack of time to add anything else to it. Be as polite a you can without being accusatory or bitter. Consider sending a copy of the email as well.

If she is the one (not your dad) pushing you to get a job, maybe he doesn't even know what's going on with that. In any event, she is his GF, nothing more, and has no authority over what she can demand of you. It sounds like she demands plenty as it is.

Keep up with what you can keep up, as it is now. Maybe try spending more time outside the house, while your dad is not home. Can you go and study at a friends house for example, even a few hours, a couple of evenings a week.

Other than letting your father know what's going on, and keeping everything honest as far as your life is now, with the main point being a part time job, that is all you can do. If you say things as you've described in your post, if he is a reasonable person at all, he will not make the same demands, or add to the demands his GF puts on you. That way you'll have a little breathing room while you finish up the next few years, in order to be out, and on with your own life.