Don't worry, I'm a girl as well but have been doing most minor work and maintenance on my own car since I started driving. Usually after you rotate them once and tighten to appropriate torque you shouldn't have a problem. The other nice thing about Mini is that they are low so you don't have to lift the tires much. I get them lined up and use something for leverage slid under the tire to lift it into place.

I do rotate my tires, every 3,000-4,000 miles. It's also a good habit because you get to check your brakes every so often.