I think it's more the fact you've been TOLD you've got to do a LFT if you want to attend & like you say, in a social setting with people you don't know is a bit odd. Why can't you do a test at home beforehand & log your result so you get the NHS text you can show her when you get there? I'd not be sticking bloody swabs down my throat poking about & gipping in front of strangers either.
The food thing is ridiculous, if she's having a party she should be catering for you, how rude. Fine to take any extras you want & your drink.
My biggest thing would be the fact she'd given out my number to strangers without my permission. That's not on, I'd be really cross. So all ways round I'd say you need to stop at home and save yourself all the hassle