I have a young bitch who is 15 months old and she's the skinniest ever.

She's still on 3 meals a day and I've changed her food a couple of times to see if that would help, but none of them put weight on her.
I've tried James Wellbeloved, Chudleighs and now she's on Harringtons all dried kibble. I've also put Natures diet on top of the kibble which she loves, but it didn't make any difference to her weight.

The vet says she's healthy just on the thin side, and she's up to date on worming.

Personality wise she's very nervous so I don't know if this isn't helping.

She feels sharp when you touch her if you know what I mean and I don't like it!
Any ideas what else I could try would be very welcome.

Have you tried adding raw minced tripe to her meals?  I find this very good for youngsters going through the 'leggy and skinny' stage.  It seems to help with adding a bit of weight without upsetting tums.  I just use the frozen 'Freeflow' Mince.  It used to be called Prize Choice but is now labelled Natures Menu.  Very easy to use.  I just shake out the amount I want to use each day so the delightful tripe smell is minimised!  I get it from my local pet shop.

Might be worth a try!

As already said protein foods will help to build muscle and bulk out a dog, throw in some raw meats, chicken wings, mince meat as already said and tripe, depending on breed you probably have an adolescent here renown for often being on the slim side, adolescents burn energy like coal, some more so than others, pretty normal until fully mature, which is why your vet is not worried, she may stay very slim until 2-3yrs then fill out, very normal, so please do not worry.

This can also be due to breeding lines as well though, some lines will stay extra slim and that is down to the breeders genetic choices made, not much you can do in that case.

But, on the whole it is generally just adolescence, as long as the diet is good, exercise and health are tip top, don't worry, you just have to wait it out, she won't be bothered by it, she'll feel fit and healthy, it's only us who feel uncomfortable ;-) once mature she'll fill out some. :-)

Chicken wings tends to add weight on very easily. Also if you just go down the route of complete foods, the one reason for why I didn't ever feed Royal Canin regularly was because when I tried it (twice), the dogs gained far too much weight too easily, so that's another option to try.

Thanks everyone for the replies....

I wouldn't mind trying some chicken wings but she's a real Hoover, anything that's not kibble goes strait down without chewing and I'm a bit worried a chicken wing would and it'd get stuck on the way down, or even back up!

If I were to brave it, would she just have the one? I know I would start her on just the one but would I need to increase it after a few days or so?

I haven't ever given my dogs anything raw before.

My girls hoover chicken wings whole so I get necks, mush better as the bones are very small, one crunch and they are gone. If I ever have wings I get a large pair of secateurs and break the bones through the skin but leave them whole if you see what I mean . That way I do not worry about larger bones in the gut. They do fine with them like that.
Aileen

You could also try breast of lamb. Many large supermarkets sell it already boned and rolled and you can cut it to the size and amounts you want.  I do that, bag it in portions and then freeze them.