Hi there

since you are just a beginning mtb, i suggested getting something with at least front suspension. make sure you are able to compress the shock as well. A lot of shocks out there are made for heavier riders. this is where some women specific bikes come in handy. the manufacturer has already taken into account the ligher rider. Comfort is very important, so when you test ride your bike, make sure you can read the handle bars with out being over stretched. Also make sure seat height and angle are adjusted properly. Shifting (rapid fire or grip) is a personal preference. i think a person can get used to either. For better performance i also suggest getting clipless pedals and shoes. you may fall over a few times, but it will make riding much more enjoyable over all.

back to suspension, don't get pushed into buying full suspension. unless you plan on being a rough rider straight off, you are better off developing your skills first.

i think the most important thing in choosing a bike is comfort. try some different bikes, and see how they feel.

i wouldn't go with a hybrid. i haven't heard anything good about them. if you plan on riding both road and mtb, buy some slick tires. i actually had a second wheel set for my slicks. very convenient. hmmm i think this is all the advice i can think of for now.

good luck