She's probably on the lower end of high tier or somewhere towards the top of mid.
She's a flexible character, but has no real strengths. If attributes were rates from D, C, B, A, S where D is the worst and S is the best, her best attributes would probably be in the B to A range where many characters have at least one attribute in S.
This is my opinion on her attributes.
Weight: C
Floatiness: A
Fast Fall: C
Air mobility: B
Short Hop: D
Priority (air): B-A
Priority (ground): C-B
Attack speed (start up): B-A
Attack speed (lag): C-A (D for grab, f-smash, and d-air)
Range: B-A (Side+B and up+B are S but overall she only has okay range)
Projectile: C (mostly unusable against other characters with projectiles)
Combos: B-A
Recovery: A
KO potential: B
Dodging/rolling: D-C
Overall offensive options: B-A
Overall defensive options: D-C
Overall survivability: B
The problem really comes down to her range, attack speed (start up and lag), and priority. Once people get too close for side+B (since it's somewhat slow), anyone with S speed attacks or S rank priority will tear her a new one. She also tends to have difficulty with characters who have good projectiles. Also, there are several characters with a bit shorter reach than her side+B, but their attacks come out faster, allowing them to close just enough distance to hit you while you try to side+B, while other characters have enough air mobility to make it near impossible to land side+B's. She also has an innate weakness against short characters as they are much more difficult to hit with most of her moves, which generally have fairly small and picky hitboxes (for not having sweet spots).
All of this is in my opinion, of course.