Reddit mentions of Peaceable Kingdom Butterflies Glow in The Dark 6.25" Lock and Key, Lined Page Diary for Kids

You've already gotten lots of great advice here, but just throwing out a couple more ideas...

• Play a game like "red light/green light" but with talking. Explain the rules of this exciting new game: when I say "talking time", you have to talk as much as you can until I say "quiet time", and then you have to be totally quiet until the next "talking time". Start out with very short "quiet times" so she can be successful, and then you can challenge her with longer and longer times as she gets better at it. Might not give you much of a break in the short-term, but at least it starts letting her practice self-control over her talking.
  
  
• Another game: the "listening game!" Challenge her to see how many sounds she can hear in different locations (the kitchen, the bedroom, the backyard, etc). Listen with her for a set amount of time (maybe show her a timer so she can see how long is left; again, work up to longer times), then discuss all the different sounds you heard.
  
  
• There are a couple good picture books on this theme that you might read with her, such as Lacey Walker Nonstop Talker, My Mouth is a Volcano, and Howard B. Wigglebottom Learns to Listen. You might also check out The Listening Walk or Silence before playing the above-mentioned "listening game."
  
  
• Maybe reframe the problem as working on listening, rather than talking less. Play some games to practice listening skills, like being a robot who follows directions (of course she gets to take a turn giving you directions too!), or listening to music and drawing/painting what it sounds like to her.
  
  
• Try some relaxation or meditation exercises - this site has some cool ideas, and there are quite a variety of apps out there too. One exercise that I love doing with kids this age is mindful eating - have her eat a chocolate chip by letting it slowly melt on her tongue, or eat an orange slice as slowly as she possibly can. Guided imagery can be fun too, though again you might have to start with something really short. Imaginations and Starbright are both collections of brief guided imagery stories; there are also recordings such as Still Quiet Place and Indigo Ocean Dreams. I've also heard good things about the book Sitting Still Like a Frog.
  
  
• Love the "brain voice" idea that others have mentioned. Maybe you could practice using your brain voices together, like agree you're both going to say the ABCs in your heads at the same time (you can kind of bob your head or something to show that you're thinking each letter, to help her go through them all slowly). Have her try singing songs in her head, reading signs or short sentences in her head, etc.
  
  
• Not exactly a long-term solution, but you could try to find her some other listeners besides you! When she's talking your ear off, tell her to go talk to her brother, or the dog, or her favorite stuffed animal. As she gets better at writing, she can write letters to friends (or you!), and journal to herself. In fact, it might be worth getting her a fun exciting diary now (something like this) even if it's a bit laborious for her at this point; at least maybe she'll be quiet focusing on her writing!