Muscle twitching in the absence of muscle weakness and wasting is unlikely to be ALS. ALS is very rare, particularly in a 27 year old female. Muscle twitching is more commonly assocaited with an overactive thyroid gland, a normal response to cold, exercise or certain medications, due to a pinched nerve, or more rarelydue to some spinal cord problems like syringomyelia or viral infections. It can also occur as a benign syndrome with or without muscle cramps.
Pinched nerves to the leg can be looked for either by EMG or by MRI scan of the lumbosacral region.
Good luck
This may just be benign fasciculations that people sometimes experience. These can progress to other parts of the body, but if you do not experience any weakness accompanied with them and no other problems, such as weight loss, etc. there is probably nothing to worry about. But to ease your fears, have another EMG done in a year or so.