Start talking to her about something then wait for a lull in the conversation. You could casually slip it in like it's not a big deal, that way she'll be more inclined to accept it and not make a big fuss. I can't make any garuntees, but it usually works for when I tell people.
I wrote a letter to my mom. After a few days I talked to her about the letter. She said that she still loved me but she didn't agree with that "lifestyle". My only advice is do it only when you are ready. Don't let people pressure you to come out.
You could also just tell her, you don't have to write a letter. It'll be hard of course but there's no easy way to go about this.
What he said. Whether you tackle it head-on or do it in a letter, do it when you're ready, not on someone else's timetable.
A few things I would suggest: Do it when you are both in a good mood. Especially her, as you are more likely to not have a better reaction than if you catch her when she's on edge. Try and slip it in a conversation. If you say something like, "we need to sit down, I have something to tell you" it can give her the impression it's some big shocking news and may put her on edge (being LGBT of course shouldn't be shocking to anyone but hey). Finally, think about what you want to say. You may even want to practice a couple of times. (I did this when I came out as bisexual to my mother). Also think about the type of questions she may ask so you can answer them without stressing. These may include such things like, how long have you known? Etc. also be prepared for for thing she may say, including disbelief, It sometimes takes time for them to get used to it and accept it. Of course, she may just accept it and be happy and all is well (hopefully). Hope this helps...
Just to let y'all know. I came out to my brother and he was really good about it. I haven't come out to my mum yet but it's a step in the right direction
Take it slowly and don't throw multiple bombshells at her in a short space of time. And be open and stress that you're the same person as before, and if she wants to talk you'll be there.