I don't think noise or vibrations will be that big a deal. DW sits at our dinette and surfs the internet while I am going down the expressway.
However, I don't think a Class C will be big enough for you. I KNOW a Class B won't be. We have a 32 foot Class C for just the two of us. We camp for 2 to 3 weeks at a time, and if the weather is bad forcing us inside, we get very crowded. I wouldn't dream of adding a teenage girl to that mix.
The suggestion of outlining 300 square feet in your home and living in it for a while is very good. However, remember that 300 square feet has to include both the bathroom and kitchen.
Seriously, take masking tape and tape off that size area. And 300 square feet is generous. My RV is closer to 240 square feet inside.