17mo old girl, 19 lbs, wakes up middle of night asking for food each hour.   I feed her and she eats a little and then sleeps. Ok or a bad habit?

Bad habit. She should fulfill all her nutritional requirements during the day. Waking up and asking for food is probably just a bad habit that needs to be removed for your and her sake. Talk to your doctor about how to improve her sleep hygiene. Tough love might be the only way.
I'd want to evaluate. A kid eating that often could have developed a night grazing habit or may be compensating for a real metabolic issue.A 17mo at that wt is on the lighter side of normal so both factors give me more questions than answers. A few basic tests and review of her growth pattern is warrented. If ok your provider should help you develop a plan for more restful nights.