Ariel Winter's BFF Sterling Beaumon -- She's BETTER OFF with Her Sister

"Modern Family" star Ariel Winter is in a "much better situation" now that she's away from her mother and living with her older sister ... this according to one of Ariel's closest friends.

TMZ spoke with Sterling Beaumon -- a fellow child star who met Ariel on the set of a Nintendo commercial a few years ago. He also starred as a young Ben Linus on "Lost."

Beaumon tells us he's still very tight with Ariel -- and has had extensive conversations with the 14-year-old actress since a judge removed her from her mother's home and named her older sister Shanelle as her temporary guardian.

"Everything is good with her," Sterling said ... "She's in a much better situation now."

He adds, "I actually know her sister as well ... her sister is a wonderful girl, woman actually ... great person. "

When asked about allegations that Ariel's mother Chrystal has abused the actress both mentally and physically ... Sterling said, "I can say that [Ariel is] not lying ... there's no reason for her to lie about something like this."