The only thing I could find regarding Sirolimus was a clinical trial. I've never heard of it before. It seems to be used mostly for children who have 'cytopenias' due to ALPS.
www.clinicaltrials.gov/ct2/show/NCT00392951
I don't know anything about your daughter's situation or how her symptoms are when counts are down. I do know that many doctors are trending towards the 'watch and wait' method which means no treatment unless symptoms are present. Many children do fine with that if the doctor and parents are on board. There have been several parents here who chose that route and have been successful with it. I'm not advocating that for you, just mentioning it. Many children have eventually obtained remission with no treatment intervention. Sirolimus seems to be a somewhat drastic way to go at this point since I'm not sure that you've done the first and second line treatments yet. It's not necessary to normalize counts when one has ITP. That was the thinking years ago but things have changed.
I know you want to make the best possible decision for your daughter and that would be very hard to do. I have been involved with the PDSA since 1997 and have followed
every patient who has come here since then. It all boils down to benefit vs risk. Only you can weigh the pros and cons of treatment risk vs ITP risk.