Thanks for pointers. Looking at the m&s website, they have a few options which are a cross between a bra & cropped top, so have ordered a couple of those. These also come in age rather than size. Not sure she's quite ready the right size for an actual bra .
Have also ordered her a sports cropped top as she runs a lot.
Matalan also do a nice compromise crop top/bra type thing that dd also 11 is prepared to wear. She will also wear a soft sports bra type thing as well. The ones that are more like a crop top with some cuppage rather than an actual bra shape if that makes sense.