I understand your situation and how you want to start working to make some money, but a high school diploma is definitely worth more than a GED. Working instead of going to school might make you some money right now, but in the long run you will be losing a lot more than money by not finishing high school. You're a senior, so what's one more year? It does sound like you have a very busy schedule, but sometimes you just have to do what you have to do.
As far as the depression you mentioned, I want to encourage you to reach out to someone whether it is in your school, friends, or family. Even if talking to someone about your problems may sound lame, it can really help. There should be plenty of people in your school to talk to that will be completely unbiased and will pass no judgment, so that will be a plus. Don't be afraid of approaching someone, it's their jobs to help you. They all went to school, got degrees, and probably paid ridiculous amounts of money to be where they are, so helping you in any way or just giving an ear to listen to what you have to say is not something that is a burden or annoyance to them.
If you ABSOLUTELY have no other solution but to drop out, I think you should discuss it with your parents and make that decision with them. Although there is a 99% chance that they will discourage you from dropping out, there is always a chance that they will agree with you (if you have a REALLY good plan in motion), or maybe she will take the burden off of your shoulders and give you reason not to worry about your financial problems.
Just keep in mind that at the end of the day, all anyone wants for you is happiness, whether they are your parents, siblings, teachers, guidance counselors, friends, etc. Sometimes it's better to look at disagreements this way rather than think that people are against you. Good luck :)