Why is that relevant? There's no correlation.
This is always a difficult scenario as it's very very costly to buy new skates every few months as your feet grow, especially if you hit growth spurts.
The best thing from a performance as well as value standpoint is for you to be fitted properly by a store given that you will be growing. They should be able to put you in a size that's bigger than your true size now, but not too big as to impact comfort and performance.
Why did she say that the skate size might be hampering you?
Well, that could be due to the poor quality of the rental, not necessarily the skate size. While skate fit is paramount, you need to consider the fact that parents cannot and do not want to spend on skates every few months. Everyone needs to find a happy medium.