Bianca and her mom, Alexandra, hit up a cosmetics store in the San Fernando Valley, and she loose again ... no bra underneath a skimpy pink mini-dress.

The mother-daughter duo has been spending time together lately, hitting up Rolling Loud in L.A. Thursday night to watch Kanye perform. Kim Kardashian was also front and center ... we don't know if they talked, but they clearly have lots to talk about!

Bianca and Kim have been showing up at the same events ... 2 days before Rolling Loud, they were at Kanye and Ty Dolla $ign's "Vultures" listening party in San Francisco.

Our sources say North West is top of Kim's mind these days. The kid's fully in on Kanye's new album -- both in terms of performing at events and recording -- and we're told Kim's concerned about keeping her daughter grounded and free from toxic conversation.