If its pronounced like that that that's what i'll say. I used to call her Mere-en-jay before I realized what she was actually pronounced as, which certainly isn't today.
Off Topic, but Fun Fact:
Did you know I nicknamed Slurpuff after this NL villager in Pokemon Y?
I pronounce it like the Spanish word, so 'mer-en-gay'. If her name was spelled 'meringue', then I'd pronounce it like the dessert, which is probably how you're supposed to say her name anyway seeing as she's a cake rhino