I think it is ok not to have headspace and hold boundaries, the way in which you deliver that information is what is important. For example she could have a stock message that goes out yet feels personal. Could say something like, 'I am so sorry for what you are going through, unfortunately I too am struggling and therefore feel like I'm not well placed to help you at the moment for your own mental health as well as my own. I'm so sorry. I have found these organisations really useful *signpost* and recommend you get in touch with them. I hope they are useful for you too. I hope we may be able to connect in the future when I am feeling in a better place. Love Elle.'
It isn't that difficult if I can write it in 30 seconds it can be done. She could also have a similar post to give people a heads up. Ultimately most people are understanding. The coldness of replies and the direction to her books is what is off putting.
It may even help those that are struggling find more appropriate care and/or community of support. Which could make, I'm sure, the world of difference.
For balance I have had quite thoughtful replies from her. But am sorry for those that haven't xx