Haha, well honestly, she's how she usually is XD.
Not much you can do at Lil Shop of Horrors yet. She's mainly a tease/placeholder for future content. If she isn't selling you the transforming clothes, then you need to get them somewhere else (try visiting someone in Transylvania)!
The third time, she's just standing there at the entrance. Though you need to sleep first before she appears.
Glad you liked seeing them there at Roxie's XD. Definitely trying to do more casual random encounters like that.