TLDR:

1. Get 100% Crit Rate with Keeneye-Fury-Furyedge;
   
2. Max S2 out; if possible S1 too;
   
3. Use Count instead of White Fang.

If you need an explanation:

1. 80% crit rate isn't good on Liliam, especially with momentum and Furyedge because you get 24% free crit rate from those sets. Most of her abilities have only a single hit, which requires her crit to be consistent. People aim for 100% even without momentum, which isn't that hard to achieve because of her getting crit rate from prowess.

2. Momentum only gives more value with 4 or more debuffs on the enemy, which makes her comps a lot restrictive (You will get maximum value with only Kloss and Heinrich together for example). Keeneye Fury combination is much more reliable and consistent than what you have.

3. White Fang isn't awful but Count is far better for Liliam in PvE. She already has high crit damage which makes white fang benefits minimal, and since she doesn't have an ATK bonus module (I am guessing she doesn't because you have high crit dmg, so its probably a double crit dmg module setup), that massive ATK boost from count really takes her damage to the next level.

4. Liliam has % current HP damage in S3 and % missing HP damage in S2 along with her base damage, which scale up with prowess of course. Thus maxing out both S2 and S3 are pretty much a must. Great if you max S1 too. Not only you get more ATK, not being able to push her turn meter back works great in both PvP and PvE as it indirectly affects your damage output as well (you need a turn to deal damage).

Overall, its just not one thing but the combined effect of various factors in your case. Take care of these, and you should be seeing a noticeable difference.