Milania Giudice is wishing her "best big sister" Gabriella Giudice a happy birthday ... just months after the birthday girl called the cops on her before her assault arrest.

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In a sweet birthday post for Gabriella's big day ... Milania admitted that she has put Gabriella "through a lot over the years."

Milania added ... "I know I haven't always made being my sister easy, but you've always been there for me, accepted me, and loved me through everything."

Gabriella -- who was the one to dial 911 on the day of Milania's arrest, telling officers her little sister was acting erratically and throwing food and candles inside Teresa's New Jersey mansion -- was even called Milania's "fav sister" in her birthday tribute.

Milania's post comes after what family matriarch Teresa Giudice called an "incredibly difficult" time for the family.

After a tense incident at Tampa International Airport involving Milania, Teresa, and Gia ... Teresa cleared the air on social media following Milania's meltdown, explaining that her daughter suffers from "significant psychological trauma."

In the footage obtained by TMZ ... Teresa told officers that Milania had "fentanyl" in her system ... with Milania claiming she had been "laced."