Heather could NOT have looked happier Friday celebrating her daughter Ava's 22nd birthday in WeHo at Fig and Olive. Coming along for the ride -- Chris Heisse, Heather's ex, though it appears they're back on despite a tumultuous history.

Ava wasn't riding third wheel ... the birthday girl appeared to also have a date. Regardless of their troubled history ... seems they all had a great time hanging for a little fam-bam sesh.

As we've reported ... Ava in the past had been "concerned and sad" over her mom's mental struggles. They made up last year and even hung out on Mother's Day. Heather, of course, spent 30 days in a residential mental health facility as ordered by the judge.

That move meant Heather would avoid jail after pleading no contest to 8 misdemeanors, including 6 involving battery on a police officer or EMT.