I used to play her, too, and is was for this reason that I ended up dropping her. It got to the point where she was dull even for me. She does tend to have dull or unwitty dialog in canon, which makes it especially difficult to rp her, but making her more interesting can be done. Emphasize her politeness towards Remilia, Patchouli, and Flandre, while emphasizing her bluntness while remaining polite towards anyone who's not the aforementioned. Those in the SDM are the only ones she will genuinely care about.