Female - 22 Years Old
There is no such thing as "class-related playful texting." Playful/flirty texting is playful/flirty texting. Maybe she's shy and it's less awkward for her to flirt over text if it's "class related."
edit: It could be that she's interested in you, but she's not sure if you're interested in her back or whatever, so she's kinda holding back.