Sometimes people can't even think straight when they are under extraordinary stress- it honestly may have slipped her mind that she has no heard from you for a while because, frankly, it sounds like her life is pretty much falling apart right now.

Is she leaning on you constantly now that you are sick and demanding your time and energy?

If not, it could also be that she has concluded you are both ill and need to tend after yourselves, lest you take eachother down completely.

If you really care about someone, like truly deeply care and love, trust and respect them- sometimes you have to deal with them being selfish because they need to take care of themselves.

People are extraordinarily imperfect and when you accept someone as being a loved one, you accept that sometimes, even often, the "scale" of the relationship will seem completely uneven.

A good relationship of any kind means that you don't do math. It's that you give what you can when you can without sacrificing your own mental or physical health- because if you do that, you are of no use to anyone.

The whole tit for tat idea... if you look at it superficially as in "when she was sick for x amount of time, I did 1,2,3 but she hasn't even done one and I have been sick for x+3 amount of time"... it is guaranteed to breed resentment and create major distance.

It isn't about that and shouldn't be. Yes there will be times when people who care about you and who you care about won't be around to support you in the ways that you need even if they know what you need and really truly want to.

It sucks, but depending on how much you have invested in this relationship, I would attempt to take a broader view.

If she was just diagnosed with diabetes, is having panic attacks and who knows whatever else- that is truly life-changing. It basically means she has to upend her entire life- how she eats, what environments she feels are safe to be in, what she does everyday, and also she has to, at least for now, exercise extreme control over how she interacts with the world and who she interacts with.

A combination of panic attacks and diabetes quite honestly has a potential to be fatal.
I understand that you are also dealing with a lot of stress but ultimately in our social circles, we can spread out what we take and give and it comes back around. If you can't rely on this BFF right now, rely on your husband. If you can't find anyone, shore up your inner strength, spend some "me" time learning about diabetes maybe [I don't know what your personal knowledge is].

Or do something entirely for yourself.
She will break out of whatever issues she is having, but trying to force someone to get their life together, or playing "this is worse than that" or even comparing your anxiety to hers will likely only lead to major conflict.

Investment in a good relationship is not about the short term. It isn't about any kind of return you receive today or this week. It is about long term stability, health, welfare, love... so what you did yesterday may not seem appreciated in a real tangible way until two years from now.

I understand it is really frustrating when you feel like you have done your part in a relationship, but it is also important to consider context and situations and to actually give someone the opportunity to do their part also.

It doesn't sound like your friend is in the best position to be able to demonstrate she is a friend right now.