Cats communicate with each other and you, their owner, using a wide variety of sounds and body language. With a bit of study and observation, you should be able to work out exactly what she is trying to tell you.
Cats are capable of making a wide variety of sounds, ranging from howls and purrs to chirping noises. Here is a quick guide some basic cat sounds and what they mean;
Meowing is the most common sound a cat will make, and can mean any one of a number of things depending on tone, pitch or volume. A soft meow is usually a greeting to her owner or a cat companion. If the meow is more strident in tone, it is usually a demand for something, ie food or attention. The louder and more strident the tone, the more urgent the demand. A repeated, loud meow is a very strong demand and is very difficult to ignore. However, she will sometimes use a soft, higher pitched tone if she is asking more politely.
A scream will indicate that she is in pain, or very distressed. Screeching is used when emotions are running high, such as prior to a fight. And we have all heard the unearthly wailing of two cats trying to intimidate each other prior to conflict- often in the middle of the night!
A purr is used to show contentment, although cats have also been known to purr when injured. It is thought that the vibration purring causes aids the healing process and soothes cats. If she meows whilst she is purring, she is feeling very relaxed and content.
A cat will growl as a warning, for instance if you are playing with her and she wants you to stop. Persistence will usually result in physical attack, so be warned. Hissing is used as a serious warning or intimidation; the cat's next move would almost certainly result in an attack.
A soft chirruping call (known as the chudder) is used to attract attention, or as a gentle greeting. You may see your cat watching birds through the window, and making an odd little 'chattering' sound. This is very common when they are watching prey they cannot reach, and it is not known whether this is meant as a threatening sound or caused by frustration.
Domestic cats tend to vocalise more than cats in the wild, probably because they have learned that this is the best way of attracting human attention. If you observe your cat over a number of weeks, you should become very familiar with her own unique 'vocabulary'.