Wow! Without that tattoo - you'de never know she was spayed! you can't see even a hint of a scar (at least on the pic).
I thought about having my dogs tattooed with the words - "I have a microchip" too. Just so if someone steals them then eventually surrenders them to a shelter, the shelter staff will know to scan for a chip. Some shelters around here will ask if the person surrendering a dog/cat has a chip. If they tell them No, the shelter wont bother scanning them for one. When I worked at the local shelter, I was the only one who scanned for chips regardless of what the "owner" told us. Found a few chips too that we weren't told about. Most came back to the breeder (breeders are required to have identification on their dogs - either chips, tags, or tattoos)