At 5 months of age, a sippy cup is not appropriate. At that age, breast feeding is best, or formula from a bottle. It sounds as though you're rushing her (putting baby puff finger foods on her tray every time she's in the high chair, for example, and giving her mashed potatoes).
She's 11 months old. It takes time to develop the skill of eating. It involves getting those little fingers to grasp a food, then finding that mouth, getting the food in, using the tongue to move the food to the right place, and often there are no teeth (or few teeth) to help). It's a complicated process.
Relax, don't rush her, make sure she's getting the right nutrition. Ask your pediatrician if she's getting enough food, growing in a healthy way, and what foods or formula or breast milk she should be consuming.