Well, I can't say I have much expertise with regards to costume crafting - that's my mother's job. However, I find that improvising can help.
[spoiler]For example, last Halloween I went as The Hitcher from The Mighty Boosh (Google it). I bought a top hat, long blonde wig and face paint (I needed green, but they had none, so I settled for pale blue) from a costume shop, borrowed my mother's black fur coat and red scarf for the outfit, snipped the fingers off an old pair of black gloves for the tramp gloves and painted a spool of sellotape white with Tippex for the Polo mint monocle, which I had to tape to my glasses. I also bought a pack of Polo mints and glued them all around the rim of the top hat, since Polo's are a staple of The Hitcher's design. All in all, it turned out quite well.[/spoiler]
The point is, don't go overboard trying to find something to suit it. For the shirt, maybe a large white vest with the sleeves cut off? You could get some yellow craft paper and cut a bunch of frills out, then glue them onto the shirt (tedious, but if ya want authentic, ya gotta work for it). For her necktie thing-a-ma-jig, I'd say you should use whatever you made the bow out of and just dye it yellow, then clip or staple it to the shirt. For her collar, well, that shouldn't be hard: all you'd need is some black fabric, cut it into the right shape, make a hole for your head to fit through (or staple the collar together behind your neck) and get some yellow paint or tape for the trim. Finally, for the belt...well, I'm sure your dad might have some belts lying around. Ask if you can borro one, and if the pattern is too different, just paint it so it looks better (I don't know if painting a belt would suffice, it depends on the material, I guess).
I hope that helps. I'm not an expert on cosplay, but I reckon you'll be okay. Good luck!