We deal with the same issue from time to time with our daughter. Everyone is different so I think it really depends on their appetite. We generally make sure her after school snack is just a small one, or if I think it may be too close to dinner just say no to the snack. Another option we use is offering a fruit or vegetable so if she doesn’t eat much of her dinner at least she ate something healthy.
Many toddlers graze, this is normal. Some families have easy to reach and healthy snacks at t apace where the toddler can get them herself. A cabinet or shelf with small items she can “control” may help her to get the nutrition she needs and feel a bit more in control – you will have to control the stocking of it – not more than a serving at a time. Another thing to do is to include her in the preparing of dinner so she can take ownership and even snack as the meal is prepared so she is getting the dinner ready.