Dear Prosperity,
Have you actually suggested to her to "talk as if and act as if you are well", indicating that you make this suggestion so that her sub-conscious gets a message that it's time to heal/be well, rather than constantly re-inforcing the mind with "I am sick".
You can even blame me for this if she reacts negatively, just saying it was some information you received from a healthcare practitioner who has found that acting and speaking as if a situation is different can contribute to the outcome hoped for...
If this isn't accepted as palatable for her, then chances are she is very invested in the return she gets for her complaints (i.e., the sympathy, listening ears, get well cards etc mean more to her than regaining her health).
I agree with Ponderings that it may be time to vet your phone calls before you answer, and allow yourself some space.
Is it also possible that you worry that you might have a tendency in the desire to have someone listen to you the way she tries to make you listen to her, yet you realise this isn't a behaviour you want for yourself? Sometimes when we fall into that category, the issue grates even more. Please realise I'm not saying you're like that, just that there might be something in you that recognises the attraction to have someone listen to your woes without expecting you to listen to theirs... In other words, no exchange or fair sharing.
Good luck with it all,
Suzibeth