Mother's name in different in my documents and her documents

My all school certificates has my mother's pet name(Leena) and in my birth certificate is Sumitra, however my mother's original name is Sumitra Devi which she is carrying in all her documents. Now, i am facing problem that I can't change my mother's name in my school certificates as per the CBSE rule which says that Correction in name to the extent of correction in spelling errors, factual typographical errors in the Candidate’s name / Surname, Father’s name / Mother’s name or Guardian’s name may be made but in my case name is completely different (Leena & Sumitra Devi). Also CBSE says that the Application for correction in name of Candidate/Father’s/Mother’s/ Guardian’s name will be considered only within one year of the date of declaration of result which i have already crossed many years before. Now i have to get my mother treated in the hospital and have to claim the bills from my dept. because i am a central govt employee but the bills at hospital will be generated by my mother's original name i.e. Sumitra devi but in my department the name of my mother is Leena, so to avoid this issue i need an advice how to make the changes in the name or to prove that Leena and Sumitra devi both are the same person to avoid the problems during medical bills reimbursement. Kindly advice please.