Just a week ago this started and she thinks it's unfair for her to give you a little time, even though you're actively trying to learn and be comfortable??! She's got to slow down and realize that she's not behaving like her relationship with you is something valuable that she wants to be careful to preserve. If the feelings between her and this new guy are really so strong, they'll survive a little waiting.
Respect is the most basic thing you must have from your partner, whether you're poly or mono. If she won't give you that, I would take Mono's advice and let her leave. Better yet, flip it around and let her know that you can't stay if she refuses to acknowledge and work with your feelings. I know that sounds extreme, but the way she's pressuring you is not ok. It's emotional manipulation to get what she wants, it reminds me of a teenage boy insisting that his girlfriend get sexual right away when she wants to take it just a little bit slower. After all, this could affect your heart and your health as much as hers, she's got to take you into account if she cares about you!