Sorry, bold fail here's my post again.
I am rarely off sick unlike other people at work who seem to take weeks off at a time for ‘stress ‘. I have plenty of things in my personal life going on to make me stressed but I just get on with it
The only thing worse than your patronising quote marks on 'stress' is the fact you don't even think other people's are real, just that they should get on with it because you can.
From your tone in the bold bit above you obviously do think badly of people about it. If you judge them for being unable to just 'get on with it' then maybe you should have 'gotten on with it yourself' and asked to work from home or just come in late.
She was either oblivious to your park visit and you've massively projected this because you were already worried it didn't look great.
Or she saw it, got a bit peeved and made a comment about it, which is wrong but you should be adult enough to decide to leave it and move on, or address her directly to explain (only very quickly no scene required) that you weren't well enough to come back to work.
Whatever scenario, running to a manager to report such a minor thing looks worse for you than for her tbh. We are adults - you're allowed to correct someone's misconception and stand up for yourself.
All you get out of this is a now awkward situation with her that could've been resolved very quickly between you two directly. And also a question mark in your managers mind as to whether your judgement is poor in wasting her time on this!