Talk to Pediatric Nutritionist on Baby Not Eat And Under Weight

My baby is 15 months old she only takes 1-2 bites hardly and spit it out sometimes when she doesn't want to eat she is exclusively breastfeeding her hb and vit d is normal , her weight is 7.8 kgs what should I do to make her eat I tried everything she doesn't want to eat and drink except breast milk and water. In solids she only likes to eat popcorn. I am very worried her height is 70cm. I visited to dr they said work on solids but I have been trying for months and no luck her weight is stuck on 7.8 because she is not eating anything