They buff Elise so that she is playable and as soon as she is, they start nerfing her to make her crap again.
When asked about the current PBE nerfs to Elise's Q (dropping the target's current health % damage down to 4% from 8%), Meddler explained:
"We're nerfing the % damage in order to make Elise weaker, because we believe she's far too strong at present. Compensation buffing's not appropriate as a result, since it goes against the goals of the change. Compensation buffing can be the right approach in other contexts (e.g. removing power from a skill with little counterplay, adding it back in to a healthier spell), sometimes though what's needed is just a straight nerf."