Does the IOS7 download affect any apps?

No it depends on how many apps have.

My sister got it and all the apps look cartoon like and not nice. Really the update is ugly.

I am not getting it. Though,from the last update I got I lost all my apps ,because you need a lot of storage space for it.

In rare cases,it tells you that you need to delete so much data ,but not always.

If you have lots of apps and like it how it is I wouldn't risk it.

Anyway if you are unsure about how it looks ,then this how it looks.