Any nannies quit their job before?

Sorry this is so long, just want there to be a full understanding of my situation. But basically, I feel disrespected as a nanny with this family and want to quit, here's why.

I'm a nanny for a family with divorced parents and I watch the child at the mother's house, as she has full custody of the child. At first I loved the job and I was getting a lot of hours (30-40+) and things were going well. However, lately things have been becoming unbarable. I started in august and since about November, my hours drastically dropped. For about a month or more I was getting less than 20 hours a week (I am supposed to be a full time nanny), and after several conversations with my employer, she agreed to give me full time hours (35+ hours per week), which she did for about a week or 2, since then my hours have dropped back down and I am now getting consistently less than 30 hours a week for several months. After talking to her about needing to work at least 30 hours a week, and no less, to be able to afford to keep my job with her (we talked on Thursday last week) I was scheduled for less than 30 hours again this week and then she cut my hours on Tuesday so now I expect to get less than 25 hours this week. In addition to not having enough hours (I was brought on under the premise I would be working FULL-TIME) she had been taking advantage of my kind nature and having me do things outside of our agreement, and taking advantage of my flexible schedule. For example, she will "forget" to put the dogs in the kitchen at night, knowing that they will pee and poo in the house if they are not kept in the kitchen to sleep, so I have arrived to work and immediately had to clean several pee spots and a few poo spots on numerous occasions. So when this happens each time there will be at least 3-4 pee spots and 1-2 poo spots to clean each morning that this happens. She only "forgets" when she knows I will be there early the next morning. My only duties with the dogs are supposed to be to let them out and give them water while I'm here, but instead I am feeding them every morning and giving her diabetic dog insulin shots every morning and often having to clean poo and pee, even while she is home, in addition to the duties we agreed apon. I also was supposed to help with LIGHT house keeping and occasionally grocery shopping. 9 times out of 10 I am the one doing the shopping and I run errands for her very frequently and she expects me to deep clean the house once or twice weekly and she no longer helps with any house work (except laundry) at all and I am expected to do all of it without extra pay. I do dishes, clean floors, dust, clean bathrooms and kitchen on a daily basis or every other day (the same, but more in depth weekly) and if I don't they will remain undone until I do them and then she gets upset that the house isn't pristine when I also have to look after her child. Because of all of this I have recently been feeling sick because I suffer from anxiety that manifests in physical illness/symptoms as well as making me over think and feel miserable and unable to think about anything else. Now I know this is a long explanation, but I wanted to explain why I feel disrespected and what is driving me to the decision the quit this job. It is now affecting my physical and mental/emotional health and it is time for me to move on. I applied to a restaurant to be a server (because I will not be working in child care I do not need her recommendation) and while no formal agreements have been made, I am testing it out and starting training this weekend. If training goes well for a weekend or 2 I will be able to get the job at the restaurant and I will quit my job as a nanny. I want to give her a 2 week notice to give her time to find a replacement and I will tell her I can train my replacement if she needs it. I need advice on how to give my notice/resign from my position. I am very nervous to talk to her because I feel like she will react poorly. It is causing me a lot or anxiety and I'm feeling physically ill over it. Advice please?