This could be normal. Many people experience myoclonus, which is involuntary, brief contractions of various muscles groups, during sleep, especially during the first few minutes as they are falling asleep. This has to do with the way the brain relaxes control of certain body functions during sleep and it is nothing to worry
The only time where one would need to worry about twitching during sleep is if it is actually impairing rest. For example, if your girlfriend says that she is tired all day long despite sleeping all night, or if she says she wakes up frequently while asleep, this may be a problem.
There are a few different sleep disorders that disrupt sleep and lead to chronic daytime fatigue, and these can have a component of muscle twitching. The two most common are called period limb movement disorder (PLMD) and restless leg syndrome (RLS).
If your girlfriend feels like her twitching is interfering with rest, then she should see her primary care doctor
. She may need a referral for a sleep study in order to diagnose one of these conditions. If, on the other hand, she is not bothered by the twitching and is well rested, then there is no need to worry.