You are intimidated because like us, you don't want to ruin a great piece of fabric BUT like us, you need to face your fear and get cutting.
If you can have your MIL coach you, she can watch to see that you are cutting correctly and safely. Maybe you could start with a small project first. Like anything, a little practice goes a long way.
Also, sometimes LQS's have classes about How to Use Your Rotary Cutter. Quite often they are free.
http://www.equilter.com/cgi-bin/webc...34111112701.f3
Lastly, if you are concerned that your ruler might slip, giving you a wonky cut, back your ruler with Omnigrid InvisiGrip. This is the best product!!! It really keeps your ruler from slipping. I really wish this was available when I was new to rotary cutting.