My eight years old daughter is somewhat under weight and doesnt eat much. is it ok to give her ensure as a supplement ? (just the regular version and not the max version?

In the short term this is fine. However, if she is truly under-weight her doc needs to see her and see if there is a medical reason for the issue.

A virtual consult with Healthtap is available. Review the growth chart over time. If you add calories, weight gain is expected. There is a children's Ensure available. Does she have any additional symptoms? Watch for signs of shortness of breath and vomiting.