Pre-wedding blues - family getting me down
Bless you! It does sound like its all just getting a bit much and everything is compounding to make every small thing seem massive - totally understandable!!
Why don't you 'curl up in a ball' tonight - just let yourself feel a bit sorry for yourself - go to bed early, have a long bath, eat a whole tub of ben and jerrys or drink some wine - whatever will cheer you up really!
My other advice would be stop spending energy on someone if your getting nothing back - if she'll kick off its not worth sacking her but if you leave the ball in her court and she doesnt sort a dress then she's sacked herself essentially - leave her to it and engage with her as little as possible! Don't stress yourself out over it - if you will need to pay for her trial either way then its her loss if she doesn't go - its super annoyoing as you've wasted the money but its too late now so try not to let it be any more of a waste by ruining the planning and excitement for you!