First, I think there are a LOT of better photographers (esp portrait) on this forum than myself. Pookie, Pabst, Tabor, RL, Dustin, et al. That's a very abbreviated list. There are MANY more.) I'm looking forward to what they might say.
If it was me doing it... God help you!! I would have shot a LOT MORE images. Lens? Camera? In this case, if it's spur of the moment, it doesn't matter. Get shots. The quandary that you faced is exactly why I like to carry two bodies to some events, one with a wide and one with a long lens. Ie: One with a 70-200 f/2.8 II and the other with a 24-70 f/2.8 II. (Or some other lens variation depending on indoor, outdoor, light levels, etc.)
In this case, if you could have planned ahead of time, fine... fret over lenses, etc. In that case I would have likely used the same lens if it's what I had. (Now I use the 2.8 instead.) My first shots would have been up close. I like the shot you took but only as a one of many and it would have been the third or forth composition choice group of images. I agree with distant.star, you need close up images of your daughter's face with her horse. (A portrait.) Close ups of the two girls and their horses. Other angles. Maybe other apertures (depending on lens or if you are able to change lenses before they get tired of the process). You probably could have achieved all of that with the lens you had although obviously a 2.8 would have been better to blur the background. But then you risk other things being out of focus. Moving back further and using 170-200 mm @ 2.8 would have helped with the subjects being in focus and the background being less in focus. Ditto with f/4 for that matter.
My main goal in these situations is to get as many shots and as many DIFFERENT shots as I can so I can choose, pick, etc a few shots that work best later in post. Digital film is cheap! Esp if someone blinks a lot, etc. It's not as much about the lens as it is about the photographer making it work the best they can and getting all the shots they can in the time they are allowed.