Q: Sometimes my daughter will eat her food, but other days no one can make her open her mouth, even if she is really hungry. I end up mixing the food with milk and she drinks it all. I do not want her to get used to it.
A: Although I'm not sure how old your daughter is, it's perfectly normal for children -- especially toddlers -- to have times where they're more interested in exploring their environment (or doing other things!) than eating. When children go through a growth spurt, it's likely they eat more than they would normally; on the flip side, when their growth slows, so might their appetite.
Your daughter may simply be acting her age, and/or going through a period of slower growth. I agree that it's not the best idea to mix food into her milk (especially if you're mixing it in a bottle) because it's very important for your child to learn to chew different types of foods and to learn age-appropriate feeding skills. During meals and snack times, try to offer real food before giving milk.
If your daughter is generally growing well (your pediatrician can determine this based on growth charts), provide her with healthy meals and snacks at set times each day. Eat together as a family as often as possible and minimize distractions (like turning off the TV). Creating a pleasant mealtime environment, teaching your child to eat while seated at a table, and speaking positively (rather than pressuring or forcing her to eat) will hopefully set the stage for more enjoyable meals.