"My coat is too big for her."
Translation:Meu casaco é grande demais para ela.
In Portuguese we say demais. "Demasiado" is frequently seen in Spanish. "demais" comes after the adjective. A general rule: for = para, by = por. But prepostion is something particular in every language, so there aren't prepositions translated always the same way from one language to another. It's something to dig deeper in order to get it right ;)