Great kit, nice design, but she is just too weak overall.
For her default stats: + 40 base HP, + 3 base amour, +0.25 MR per level
For her abilities:
Q: increase AP ratio from 70% to 85% to the first target it hits, and remains the same for the rest.
W: increase range by 25 (sometimes it feels like it should hit when it doesn't)
E: no changes
R: increase base damage from 150/250/350 to 175/275/375 and increase AP ratio from 70% to 85%
So you might think: "these changes will make her super op" well, maybe but I'm trying to make a few points:
1 - Lissandra is simply not bulky enough to last in team-fights, especially as a battle mage.
2 - Lissandra has a lot of trouble assassinating ADC's because her burst combo doesn't deal nearly enough damage, and forget even touching that Twitch if he has a Janna/Lulu nearby.
Say what you think in the comments, but I really think Lissandra deserves these buffs.