Hi, I was wondering you used ga after mearii instead of wa[No macron is available from this terminal. Doubled vowels are used in its place.]
The Japanese word for "today" is kyoo. It can be used as a noun and as an adverb. In the former use, kyoo can be suffixed with various grammatical particles such as -wa, -ga, -o and -ni. In the latter use, kyoo stands alone in the sentence.
1. kyoo-wa nichiyoobi da. [nominal use]
Today is Sunday.
2. kyoo Mearii-ga Amerika-kara kuru. [adverbial use]
Today Mary comes from America.
For more about particles, you can check Particles section of our resource collection.