I set up my own private limited company 2 years ago, and my role is director of the company. It's a very small company and I dont have any employees. Can I receive help from the SIRS scheme?

As long as the criteria is met, you will be eligible!

Directors are not "Self-Employed" by the definition.

The government is not so willing to help out directors as this group is a vast group with most people in a comfortable position. Although not all directors are the same, quite a large share of directors are not as seriously affected by "Self Employed" (which is not just sole proprietors, but grabdrivers, taxi drivers, etc)

Do appeal though, as your sister is definitely caught in a bad situation

https://www.ntuc.com.sg/sirs/

I will go so far as to ask her to appeal for the Temporary Relief Fund if she is having difficulties for day-to-day living expenses