What great questions you have! Engineering is a great field for females. In fact, when I was at P&W my boss’s boss’s boss was a female. So there is a chance for great success in engineering!
If you are interested in machines/robots/engines, I would stick with Mechanical Engineering. I don’t think it’s necessary to double major with Aerospace engineering, unless you were 100% certain you wanted to work in the aerospace industry. The wonderful thing about ME is that it will provide you a broad overview of various industries. Because the ME coursework is so expansive it can offer you many different job opportunities (including aerospace, automotive, robotics, engines, etc). My degree is in ME and I never felt limited by it.
I understand your questions about the engineering job hours and day to day office environment. Unfortunately it really depends on where you decide to work someday. You could end up in a very progressive small company that allows their employees really flexible hours or even a very traditional corporation that is a little behind when it comes to work-life balance. These are great questions and you should really investigate companies you apply to for work or internships to see what the company culture is like. Try to find alumni from your university that work at the companies you’re interested in and ask them these great questions. Most universities have an alumni directory. The company culture is an important part of your decision on deciding where to work. When I was at P&W they were flexible with me when I needed maternity leave, but it’s not something they did very often. They don’t allow part-time telecommuting employees and that was a major factor when I decided to quit and become a stay at home mom (which I love!) In fact, we just found out we’re having identical twins – due to arrive mid-Mayish!
Also, right now I would suggest you focus on finding an internship for this summer. Try to find a company that specializes in things that interest you. It’s great for your resume but it’s also really important for you to get out in the workforce and see if robotics/engines/machines/etc are a good fit for you. And if your university offers any engineering clubs or projects (like Formula SAE, Engineers Without Boarders, etc) you should really get involved. I know they take extra time that you feel like you don’t have but it is so important to have those kinds of experiences on your resume.
Best of luck!