Manning, 29, was jailed for 35 years in 2013, three years after being arrested for leaking thousands of military and state documents to WikiLeaks.
Her sentence was commuted by former US President Barack Obama in the days before he left office.
Susan Manning, of Haverfordwest, said: "I am so proud of Chelsea."
Manning was released from Fort Leavenworth military prison in Kansas on Wednesday.
The soldier, who was born Bradley Manning in the US, moved to Pembrokeshire as a teenager with her mother after her parents divorced, and attended Tasker Milward secondary school in Haverfordwest.
She moved back to the US and joined the army. She was arrested in 2010 and later convicted of espionage for leaking 700,000 secret documents while working in Iraq.
Manning, who underwent gender transition while in prison, said she had acted to raise awareness of the impact of US military action on innocent civilians.
Mrs Manning said: "I am so proud of Chelsea and delighted she will finally be free again.
"It is going to be very hard for her to re-adjust after so long inside the prison's four walls and I'm happy she will be staying in Maryland where she has family to look out for her.
"Chelsea is so intelligent and talented, I hope she now has the chance to go to college to complete her studies, and to do and be whatever she wants. My message to Chelsea? Two words: 'Go, girl!'"
In a statement just before her release, her family in Wales and Ireland said: "Chelsea has endured seven years loss of liberty for her whistleblowing actions while those whose wrongdoing she exposed have gone unpunished.
"The shocking and abusive ill-treatment Chelsea was subjected to in Kuwait and Quantico before the trial should never have happened and the 35-year sentence handed down by the military court was a travesty of justice.
"We are naturally very relieved that this ordeal will soon be over for Chelsea and that she will be able to take up her place in society again.
"Whatever she decides to do, we are sure she will make a significant and positive contribution."
The Welsh mother of Chelsea Manning has spoken of her "delight" as the former US Army intelligence analyst is freed from military prison.