There no term for a female cat which is widely known or widely used in English. As Amanda suggests, the term 'molly' exists, but it is very rarely heard. Some people use the term 'queen', but again, this is very rare. If you said 'I like cats. I have a queen at home' or 'I like cats. I have a 'molly' at home', you would definitely confuse most native speakers. Few people would understand what you meant, and they would presume you were making a learner's mistake. You could also say 'she-cat' or 'female cat', but no native speaker would use these terms unless it were strictly necessary to state the gender. A native speaker would simply say 'I have a cat'.

Unlike other European languages which are strongly gendered, in English we see no need to specify the sex of an animal, or even of a person, unless it is particularly relevant. A cat is a cat. In most cases it's not necessary to specify. If you say 'My cat's just had kittens', it's obvious that it's a female cat. If you say 'My cat's gone missing. I haven't seen her for days', it's clear from the grammar that it's a female. There is no need to use a gender-specific noun.

'Cat' is a general term for any animal of the species - male or female.

A tomcat is a specific term for a male cat that hasn't been neutered. They're typically smelly and aggressive.

All tomcats are cats. Not all cats are tomcats.

NB You can also refer to lion, tigers etc as 'cats'.

Very interesting information. Thanks.

Amanda,   is molly a good word?

I suppose Tom from Tom and Jerry cartoon is tomcat. Am I right?