You are, objectively, not your mind. The brain is just another organ that specifically evolved to better help your “bone prison” survive. That it sometimes comes with unpleasant side-effects like existential dread is a trade-off that was deemed acceptable thousands of years before you came to existence and one which you have entirely no control over.

I enjoy the social aspect of running. Parkruns, Strava, meeting friends and getting coffee after etc.

Why do you need to be polite? If you’re direct or even rude you’re doing her a favour because it might turn her away from approaching other adults who would actually take advantage of her