Translation:This red flower is very pretty.
If this is true, then it should not accept この in other sentences with plural nouns, but it does...strange
I completely forgot これら is the plural of これ. but how does it go with the plural of the possesive この, would it be これらの？
この doesn't have plural form. so この花 can both mean "this flower" or "these flowers".
きれい is a more mature type of pretty, which is usually translated as "beautiful". かわいい is the proper translation for "cute".