The natural process is that the adult tooth comes up under the baby tooth, there by forcing the root to absorbe & thus the baby tooth becomes wobbly.
When a tooth erupts behind or infront of a baby tooth, the above doesn't happen, so the root has to absorbe by itself, which takes longer.
When a child has a fall & bangs the teeth with an object, this can force the tooth out of alignment, even just slightly. or more often than not, jolts it up. This is what may have happened in your dd's case, or it could just be her natural biology forcing it to come thruugh in the wrong place.
You say the tooth is darker, this will be because the tooth is non vital (dead) because of the knock it sustained, but this won't (imo) have a huge effect on the teething process.
Now it sounds like the adult tooth is pushing for it's natural place in the tooth alignment & pushing the baby tooth forwards. This would cause some split in the gum, but once the tooth is out, it will heal & all should be fine. She could do warm salt water mouth washes, if you think she would be able to spit it out effectively, just to keep the area clean. Be careful with brushing the area. The fact that she is not complaining of pain is a good thing!
You should not feel like you are wasting your dentists time, she is his patient, he has a duty of care to see her & will be getting paid for it. Go as many times as you like! If you are not happy, see another dentist in the practice.