Is my baby developing quick enough?

I have a 7 month old daughter but I am slighty worried about her development. I know all babies grow differently but she still cannot sit up and she is still having trouble getting food to the back of her mouth ( we feed her puree jars and porridge for 4 months +) she doesn't have any teeth yet and doesnt appear to be teething or have any on the way. Is this normal for a 7 month ( nearly 8 month old baby) ?