I haven't seen a single post where anyone from Riot will post that they will fix her, they don't even acknowledge that she needs work. Well maybe ricklessabandon, but otherwise no one does. They all act like she is perfectly balanced.
She is picked ~.7% (not even a full 1% on any given day) in ranked games over the last month.
She is picked ~1% in normal games.
There are 105 champions, so that means the average for ranked games is 9.5% since 10 unique champions have to be picked. .7% is far below the 9.5%
Edit: I want to point out that all of the top bans are picked more than Sejuani, making her even less likely to be picked. And the 9.5% doesn't take into consideration that 6 champs can't be picked.
For normal games it is a bit more difficult because 10 unique champions must be picked on draft and duplicates can be picked in non-draft unless all draft are not included or are included in ranked. I don't know the stats for draft vs. non-draft. So let's assume they are equal. That means the average is 7.1%, and she is 1%.
Being in the bottom 5 (draft and normal) means there are over 100 champions picked more frequently. That means there are 100 champions that should be looked at, evaluated, and buffed after Sejuani is fixed. Top 5 perhaps evaluated for nerfing balance, but many don't need to be nerfed, many are just favorites. Sejuani however is not a least favorite, she is simply not good enough to be played more than 1% of matches.