It sounds to me as if this kitten has now come into season, and looking for a mate, i am guessing the kitten hasnt been spayed, if so its not her fault she is acting like this, please ask your mum to get her spayed asap [if shes not] as if she got out and got pregnant,it would be dangerous for her, and also dangerous for her to get older and not be spayed

 

I agree with jaycee -- sounds like the kitten has come into season. Please ask your mum to get her spayed without delay! This is really important.

And please make sure she does not go outdoors until she has been done. She will try hard to escape, as she'll be looking for a mate, and she will be at risk of catching a dangerous sexually transmitted disease, as well of course as getting pregnant.

She is far too young for it to be safe for her have kittens. Not safe for her, and not safe for any kits she may have. And I am sure you don't want to add to the huge overpopulation of cats and kittens, unwanted in Shelters, as that would be an irresponsible thing to do.

Even if she is a indoor cat she still needs spaying, or she will be at risk of getting an infected womb (pyometra) which is something that happens to female cats who are left to call without mating.

 

I agree with everybody about spaying.
Also, introductions are a slow process. It might take months or even years for them to tolerate each other, specially with such big age difference between them.