Oh same here! My DD is now the height of a 12 year old with the waist of a 9 year old. Which doesnt seem that extreme to me, but is just skinny enough to make you adjust clothes, or have adjustable waistlines that are all bunched up, or clothes that simply fall down!
I agree about shopping in France where expectations are that kids are slimmer (although often shorter to so you have to jump the age range). I got some good bargains on Kiabi, a French store a bit like Primark.
Leggings nearly always look like pyjamas on my tall skinny DD. Thicker leggings from M&S have often been okay, I tend to avoid the shiny sports kind as they look awful when they are baggy.
Adjustable waists at M&S in Jeans can be okay, but I find there's only so much adjusting you can do.
The Gap Kids range has a tall, skinny jeans category. These have been excellent.
I also tend to look for jeggings, which are designed to be tight but end up looking a good casual fit on my DD.
I also bought my DD a decent pair of ankle boots, you can get away with trouser legs that are not really long enough more easily.
In spring and summer, my DD just wears her leggings and jeans capri style.
But don't even get me started on jogging bottoms and tights for school! Absolute nightmare getting them to fit.