She is most likely being pressured by the Elders to force you to stay to, "save" you!
They did the same thing to me when my daughter was thinking about baptism. I talked her out of it because she was doing it to fit in with her friends and not because she really believed. I was a member of the servant body then, but I did not want her doing it for the wrong reason. I did not think God wanted the unwilling. But the God I worship is not an extortioner. The WTS god is a petty, jealous, spite filled god who wants people frightened or guilted into serving him.
Explain to your Mom that at some point we each have to decide for ourselves what is best. God gave us free will and using extortion is not something a loving God would ever condone! Can we fool God? Would He not know if our heart was not in it? Even the government recognizes that at 18 you can enter into contracts or be sent off to war. Should you not be able to think for yourself about spiritual things? Ask her to just be there for you and love you and thank her for her love and concern. The WTS dupes will tell her to get you to agree for a set period of time to come to all the meeting and go in service, and after that time you can do what you want. I do not recommend this tactic, Mom has proven that she will not honor this. You gave the WTS all those years, you owe then no more.
Remember they have no problem lying to you to save you.