I can only offer a bit of advice on thius subject, and thats simply it because what works for one child does not always work for another.
Katelynn was always my ill child. James other then occasional tummy aches when little in most ways seemed healthy, hind sight now shows me just how wrong I was but I presumed his tummy aches was jealousy etc attention grabbing concepts from him due to fact his sister was so ill.
Katelynn once James started to become so ill seemed to suddenly get worse. Her knee's hurt more her legs her you name it.
In both cases I was wrong. James obviosuly turned out to be seriosuly ill and Katelynn turned out to have a hallow bone in her knee and will most likely end up with a knee replacement once she has finished growing.
My ramble on this is , I know a small ache can sometimes seem to be attention getting, and it may be that the child simply needs a bit of extra attention but it may also be that there is something actually happening. I would double check that it isn't anything first ( I;m sure you have just saying in case because it took me awhile)
If it turned out not to be anything wrong have you thought of big brother big sister for her? Many think it's for kids from broken homes or lacking brother and sisters and thats not always the case. Sometimes a child simply needs a way to feel special. and where she is healthy this is an option for her to feel special amongst a crew of ill kiddos that need extra attention even though we know they would trade all that attention for normalcy.
Jealousy among siblings is a normal reaction. Even Katelynn who is 17 age wise , emotionally a bit younger has had jealous moments with James on this Wish Trip. even though she is included, and the trip has been tailor made for her too and even the Big Give paid special attention to her as well she still has a moment now and then where "I was always and still am always so sick but I never had a wish granted" etc etc etc, Now I know if I persued it that Katelynn would still qualify for a wish. But as a family we have chosen not to because we do feel that both kiddos are gaining the benefits of this trip. But again the jealusy does come up now and then.
If the jealousy becomes so great that it inhibits the everyday living and the chance to enjoy all thats going on around her then maybe even counseling would help? It's alot to take on being healthy while siblings are ill, soo much guilt falls on thier shoulders even though no parent , dr or anyone involved does it. Many children just automatically start a cycle of the guilt by simply feeling angry at a moment that they are not getting the attention, then will feel guilty for what they felt, then will feel guilty they are healthy and siblings are not and that they feel greedy for wanting the attention etc etc etc vicious cycle.
I'm tired today so I hope i am putting the words out here correctly
bascially see if there is some way to make her feel extra special be it Big brothers big sisters or some other type of function etc. I am not sure if you have done what I have which many of us have but get fustrated with the one who is not currently ill and say something like , well you should be happy you don't have to deal; with x y and z

if you have it's soo normal to have done so and maybe next time one of the kiddos get jealous over another even if you do not cvompletely understand and agree with the jealousy try the empathy approach? something along the lines of validating that you hear how they feel and understand and diversion to the jealusy that comes with, I know with katelynn and James If i was in situation you are in where one had something special happening and other did not and one did not want to go I would say something like, " I know how hard it is for you that xyz123 is happening, but how cool is it that because of xyz123 you get the opportunity to experiance abc.
If I am not making sense typing this out let me know? LOL James had remicade today and that always gets me all fuzzy. but when i read yoru post i was all OMG I know what she is going through feeling etc and also if you ever need to just have someone on the outside to talk to pm me and i can give you my phone number or I can call you etc free calling on my end where I have Vonage.