All families are different but if it were me I would sit down my mom alone and explain how I felt and that you are going to get married. You stated how you felt very nicely on here and could you do similar in person with your mom? Sometimes writing what you want to say can help.
Since your mom has been in the care taker role for so long I would think it is hard for her to change. A lot of confusion and unknown. She is probably fearful too. Hopefully as she see's you are happy it will get easier.