I think she looks pretty darn good!! Of course, we can't see her move, but if she moves like you say there's certainly nothing wrong with thickness. She'll tell you if she's too thick or not as she matures. If her stride starts to shorten or if she puts too much cover over her shoulder etc., you'll know that she probably is a little too thick for a top notch breeding animal. However, I don't think that's going to happen!! She looks well balanced and, as others have said, her shoulder looks really good at this time.
Its really interesting to me how some of these calves will change over time, though. I saw a Hired Man heifer on a pasture sale in May that I would have said would make an excellent breeding heifer without getting too thick. When I talked to the people that raised and sold her, they said that she had gotten so thick that she would probably have to be considered a market animal. That's kind of what makes this business interesting. We had a Sonny/Myrtle Bo bull calf that we couldn't get anyone interested in last fall so I cut him and put him in the feedlot. I thought he'd probably be a lot better than most people thought by late spring into the summer. He got shipped a couple of weeks ago and I'm pretty sure he would have beaten anything at our county fair this year going away. He looked absolutely awesome! Wish I could have seen the carcass info. on him, he looked like he had a huge top in him!! I probably should have kept him for a bull myself!!
Good luck with your heifer--I like her!!