Private Car Sale, But I’m Not There…

I’m buying a car tomorrow, but the one issue is, I’m not home. My mom is going to complete the transaction for me in this private sale in Massachusetts.

Is she able to sign my name for me on the title and bill of sale? I assume she would need power of attorney, what’s the best way to give her that in MA?

The easier option I assume is that she does everything in her name and purchases the car for herself effectively. If she does this, can I then go and register the car in my name? I don’t want her to have to sell the car to me to do this, because then I’d pay sales tax twice. Also, if this isn’t possible and the car is registered in her name, will there be an issue when I turn 25 and need to put the car on my own insurance?