Lillends are art-loving celestial snake-people that, like so many other monsters, are mentioned only in passing in other books. That's a pity, because they are actually pretty interesting.
The chassis is pretty good. 7 outsider HD, between +4 and +10 to every stat, a reasonable fly speed, reach, some natural armor, and a single natural attack (though a very uncommon one).
Constrict and Improved Grab imply a lillend would make a good grappler. The second ability's wording is weird, though, as removing one's ability to take move (and therefore full-round) actions is generally bad.
Bard casting is bard casting. It's initially at CL 6, but getting 6th-level spells shouldn't be an issue. Note that lillends have the skills to enter quite a few bard-specific PrCs. They're only a single bard level away from entering Sublime Chord: less if you can somehow manage to get 3rd-level slots.
The SLAs are mostly low-level utility, half of which the lillend already has by virtue of its bard casting. Note that a lillend also has everything from Inspire Courage to Suggestion in terms of bardic music, allowing it to qualify for several classes and feats without dipping bard.
I think +2 LA is fine here. Lillends will still get 6th-level spells with it (or 9ths if they got SC), while somewhat curbing the advantage of a better chassis and combat ability compared to other bards. Feel free to give your opinion!