Shalla hasn't been gone for nearly as long as it seems she has. She's been around, really, although it may be true that most of her time has been spent on her side of the door.
Whether or not she's been seen around lately, when Shalla enters Milliways, a duffel bag slung across her shoulder and idly tapping away at a datapad, she doesn't seem too surprised to see it. Instead, she heads straight to the Bar and drops her bag on a stool, asking for a glass of water that never materializes. A short conversation later (through which various objects appear and then disappear) and Shalla's standing behind the Bar, hurriedly scrawling all-caps letters on the board.
She may have memorized the Aurebesh > Alphabet translation, but it appears she never learned of the existence of lower case letters.
HAPPY HOUR SPECIALSJEDI MIND TRICK
HAIRY WOOKIEE
PRINCESS PUNCH
Wiping chalk off her hands, she turns away from the board and leans against the Bar, finally taking a sip of her hard-earned water.