If I remember the numbers correctly, top level spike wave causes towers to take 2.5 times the normal damage, plus the base damage. It is really the only thing I will say that QoT does well.
She also does balls-out insane AoE damage and heals herself well, but when you look at what actually wins games, she doesn't stack up.
She doesn't survive well, she doesn't kill well, and she doesn't really help a team survive any better than Oak or EB. So many people focus on how shield is worse than heal... it doesn't remove debuffs, it doesn't benefit from armor mitigation, it doesn't do this or that, but what they forget is that Sedna heals much more off of Healing Wind and super monks than she does direct heals... Shield is a good spell with its own advantages, it's the package as a whole that needs improvement and there's skills which are obvious candidates for changes.
The biggest problem with QoT right now is that shamblers LITERALLY CANNOT ATTACK. It's absolutely impossible to gauge how effective offensively QoT could be because currently if some dude is just standing there attacking you, your base, your partners, or whatever you have to manually direct shamblers into firing range. Because they're so much bigger than nightwalkers and their turn speed was gutted along with all other minions' this patch, they seriously just spend half the battle or more spinning in circles trying to get around you, each other, and reinforcements.
QoT seems decent on paper. Spike Wave is a nice AoE snare, Ground spikes does decent damage and has a valuable debuff, shield is decent since you can prep it before combat and it can't be interrupted, but in practice nothing actually works right on this character.
Her self-healing is so powerful that she can literally completely negate the damage of any one character who doesn't have artifacts. She can win a war of attrition with any other single player... but as soon as a second player comes in and stuns, silences, or just starts adding DPS, her tiny, tiny HP pool vanishes the instant they break through the shield.
Furthermore all of her abilities take mana. I posted in another thread what I would change to make her minion build viable. The gist is that I would give her an aura that improves her HP and boosts autoattack allowing her to be useful to a team when she's not blowing through her entire mana pool. I also slash the number of points required to make shamblers worthwhile, I make shamblers actually able to attack, and I emulate the other DGs' free minion summon idea by making compost reduce the cost of shamblers and be reset to 0 stacks when new shamblers are summoned...
QoT needs help, and not just a numerical buff. The developers need to sit down and think about what they want this character to be good at, about how they want her to fight, and they need to make some major conceptual changes to Uproot, Entourage, and Compost... and I would really, really appreciate it if they'd relate some of their opinions to the playerbase so we can talk it out and help get it done right.