2 weeks notice?? help!?

First, make sure you do it in writing. The written portion need only be a quick statement that you are leaving effective {date}. You don't need to explain yourself or go into detail.

As for talking to your boss, since you seem to know her really well, you might explain the situation. If she cares about you at all, she'll be happy for you, not mad. She should understand that more money and better opportunities is just in your best interest.

She might be stressed right now, but 3 weeks is more than enough time for to hire your replacement. That someone just quit yesterday is not your fault.

Just type up your 2 week notice state your last date of employment and thank your manager for the opportunity. Place your notice in an envelope and hand deliver it to her stating that you have enjoyed working there, but you have another job opportunity lined up that you have accepted. Offer to train someone if possible for a smooth transition out.

Say "I know the timing isn't good, but I've found a new job with better opportunities."

just say, you got a new job starting and you'll stay until the new job starts