Hi !!
Elle en a beaucoup is correct
she is got a lot (of it)
en = adverbial pronoun replaces a name introduced by a partitive article as "de, du, de le, de la, de l', des"
her replaces "de glace"
it has to be between the subject and the verb
Ele a beaucoup de glace = elle en a beaucoup
"en" replaces "eau" introduced by the partitive article "de"
hope you understood my explanations !!!! :)
