I try to focus on what my lecture explain about,but she can't stop talking about her things to me...
Explain that you want to hear her story, and you will talk about it after class. And then just ignore her when the lecture starts. If she gets upset you are not paying attention, just pretend you didnt hear her and explain you were listening to the lecturer. It might be helpful if you guys could like meet for a little bit after class or get lunch or whatever, that way you can stop her every time she starts to talk and remind her that you guys can catch up over lunch, or afterwards. I mean it doesnt have to come off as mean. You can even make it a joke, just say something like, if you tell me everything now, then we wont have anything to talk about later.
Talking in class can be a huge disturbance, so I know how you feel. You should ask him or her to politely be quiet. If that doesn't work, try moving seats or doing your best to ignore it. If all this fails, talk to the person sitting next to him/her and ask them to ignore it too. The more attention the speaker gets, the more they'll do it. You could also ask the teacher/instructor to move their desk away from you.
move away... or ignore i know how you feel ''big time''
"stfu plz, i want to hear what shes saying" period