For two or three day mountain bike trips the trick is to take the least amount of stuff that you can safely get away with. This invariably means omitting a few comforts but is a worthy sacrifice... tackling wonderful singletrack while being loaded like a packhorse is not a good time.
The knack to winter riding pleasure is to manage your body temperature with different layers - typically a thermal base layer against your body, a mid-layer of insulation, and an outer shell to top it all off.
I'm not an advocate of spending too much time washing my rainwear - after all it's just going to get filthy again on the next outing, but a trip to the laundromat can be a good thing and it does allow one the opportunity to audition for the next Levis advertisement.
You need to carry enough tools and bits so you can hobble home on your wounded bike but not be laden down like a US Marine.
Ground Effect cycle clobber is constructed from a range of technical fabrics mixed and matched to (depending on conditions) keep you warm or cool, repel wind and rain, deal to sweat, minimise odours, and look sharp (always).
Mountain biking is a blast - enjoyable at a whole range of different levels of intensity and difficulty. Regretfully, bicycles are mostly designed and spec'd for testosterone-laden lads - generally bigger, heavier and more gung-ho than those on the other side of the gender divide. However, most brands sport models with women's specific geometry and components... and a paint job to make you feel special! It's also possible to tweak a standard bike to suit women equally well.