[WoodyCT]

There are a million and 1 adjustments that can be done to a mountain bike front and rear deraileur to adjust the chain and shifting.

Problem is, they aren't very obvious to those who haven't spent much time wrenching on a bike. Unless you changed the chain it probably is the right length, although it may have lengthened significantly over the years if it is old. The tolerances between the pins and links enlarge from the grit and tension, and this can screw up the shifting.

I'd suggest saving the hassle and headache and take her to a shop, especially if you want to use it sooner than later.

Good luck..