Could Breast Size Get Bigger On Fondling?

Hi Doctor, My name is Ravi 23 yrs old and my girlfriend is 19 yrs old. She is very much afraid of her breast getting bigger. She likes her breast to be normal in size. When i fondle it she likes it but afraid that it will get bigger, will it get bigger by fondling it. If yes i want to know the reason why it happens, If no let me know by what means it will get bigger. I too so much worried for her. Please reply.