With Physiotherapy and Sports Psychology, Universities will consider Biology, Physical Education and Psychology to be the most relevant (Chemistry is only considered necessary if you were to take it as an alternative to one of those subjects.) So in this case, I would say it would be fine to choose Art instead of Chemistry, especially as you already have those three most important subjects down. Having one irrelevant subject vs three relevant subjects still looks good, particularly if you do well in those three. What's ultimately most important anyway is that you're doing what YOU want to do. A Levels are optional after all, and they're all about being able to finally choose both the subjects that will enable you to gain access to your ideal course, and the subjects that you enjoy more and will consequently do well in. What would life be anyway if everyone just restricted themselves so much that they stress themselves out over things they can't handle? If you can't handle Chemistry, don't do it (especially as it's not necessary for the courses that you will be deciding between.) Like you said, you're passionate about Art.
I can relate to you about the Art (as I took it at GCSE which helped keep my anxiety and low self-esteem mute.) However I have chosen to take it at A Level because it provides not only a stress-releasing function but is also relevant to the university courses I have in mind. I was supposed to have been doing my AS Levels this year but I was so depressed that I never went in and had to drop out, and during that time, I'd chosen courses that I thought would make me look "better", which I had kept on changing my mind about as a pure result of the "what would make me look good" mindset. I too considered Chemistry at one point - but really, it isn't an essential requirement for Uni, and it isn't necessary for what you want to do either.
Hope this helps :)
