Thanks for writing to Health Care magic, I am Dr , Muhammad Ahmad , I have read your question closely, I understand your concern and will be helping you with your health related problem.
First of all I would like to tell you that in my opinion this is not heart pain , as heart pain is different from your sister seems to be having.
Here I would explain symptoms of heart Pain to you.
1) Central
Chest pain compressional in nature..
2) Gets worsened on exertion.
3) May get referred to left arm shoulder or jaw.
4) It is NOT sharp.
5) Does NOT change with breathing movements like breathing in and breathing out causes no change in the intensity and character of the pain.
6) Not pricking in nature.
7) DOES NOT change with changes in body posture.
Your sister's pain in my opinion neuro-muscular in origin which can be caused by a sore muscle , her job can also cause muscles to get tense.
This being said doctors would look deeper into the matter and will get tests done like ECG and possibly cardiac enzymes this will make things clears, having limited access to info and the patiente I can only guide you to have a beter idea.
I hope this answered your question, If you have more queries I am happy to answer you.
Regards.
Dr.Muhammad Ahmad