Blurting it out can sometimes be more effective than trying to be tactful. Sometimes when people try and be tactful they end up dressing it up as something it isnt and going round the houses, eventually not acheiving anything. Sometimes it is best to just come out with it and allow your mother to ask questions. Its whatever you feel most comfortable with.
I am so pleased that you have managed to talk to her. Hopefully now you can have regular chats about how you feel etc... so that you dont end up with a load of feelings bottled up.