Fun fact: lamias aren't actually proficient with daggers. I guess that explains why this one is wielding them two-handed.
Lamias have nine magical beast RHD, which give them reachless Large size. They have +8 strength and +2 to +4 to all other stats.
In addition to any weapons they pick up, lamias can attack with weak claws and a wisdom-reducing touch. The latter is notable for being drain, not damage, but it doesn't get iteratives and will require multiple applications to reduce even weak-willed targets to unconsciousness.
Finally, the SLAs. They're all illusions or enchantments, none of them out of reach for a caster of this level. Disguise Self is a joke: how many quadrupeds with humanoid upper bodies are there for a lamia to appear as? I can think of centaurs, wemics and maybe dracotaurs.
To be honest, I feel like lamias deserves a -0 LA. Its CR is a whopping three points lower than its ECL, its damage output is low for a ECL 9 creature, and its SLAs are outclassed. -0 for now, feedback is welcome.