How to handle this?

[Sallysitdown]

I am a lodger and LL has kindly invited me for a dinner w her friends this eve. She is very particular about this and has even started menu planning. However have stupidly just realised i agreed to visit my parents this weekend - both clash! How can I politely give my excuses?!

For obvious reasons want to tell her sooner rather than later, but equally feel so rude that it’s so last minute...!

Just pick up the phone and say what you said here. You forgot you had a clash. Don't mess about with texts, just tell her now.