She can also be asked to bite the Dragonborn, which grants the ability to become a Vampire Lord, however this cannot be done if she has been cured of vampirism. Unfortunately, the wiki is not very clear about this.

However, it is also possible for Serana to confer the power of Vampire Lord on you if she is currently your follower, and you have completed all of the main quests for the Dawguard DLC. Harkon offers this power during Bloodline, Serana offering it twice, once during Chasing Echoes, and once more upon completing Kindred Judgment. Though Werewolf wins in speed and melee damage. Generally, before the Dawnguard, if you were infected with Vampirism you would not be attacked once getting to level 4 Vampirism. This DLC came with many perks, but unfortunately, there were a few downfalls to this feature as well. Harkon or Serana can grant this power during the main questline for Dawnguard. What’s better werewolf or vampire in Skyrim However, being a vampire is overall better than a werewolf, not just because you get a sleeping bonus, but because of necromage. When the Dawnguard DLC came out for Skyrim, the option to become a vampire lord became available. Whether or not you have sided with the Dawnguard up to that point should not matter, but becoming a Vampire Lord will likely cause them to become hostile to you, which will cause them to attack you if you try and return to Fort Dawguard or interact with them.

Serana offers it to you once during that quest, and again after the quest 'Kindred Judgement'. Yes, it is possible to become a Vampire Lord after having completed the quest 'Chasing Echoes'.

Skyrim becoming a vampire lord