It gets worse in episode 8 during "The White Devil Incident" when she realizes that she ended up making the same mistake again.
Nanoha's Near-Death Experience in the flashback from episode 9. Made even more heart wrenching when they focus entirely on Nanoha as she tries to go expedite her own recovery, being in a lot of pain while trying to stand, then Shamal states at that time, her injuries may end her career and possibly cripple her for life.
In chapter 2 of the manga, Vita has a flashback to the incident. It's not pretty.
When Vivio is kidnapped, Nanoha continues to perform her duties, but after a conversation with Teana, she sees the stuffed bunny that she gave Vivio on the ground. One could feel Nanoha's pain upon seeing the look on her face when she's suddenly reminded of Vivio. Once she finishes and no longer has anything to keep her mind off it, she breaks down crying in Fate's arms. It has even more impact when you remember that this is the only time in the entire franchise that Nanoha is this emotionally broken.
Vivio: All my sadness, my pain, they were fake, created things. I can't be allowed to live!
Notably, when she refers to Nanoha and Fate during all this, she uses the honorific "san" instead of "mama". Not because she doesn't love them, but because she doesn't view herself as being human.
That one moment at the end where Vivio tells Nanoha to stay away from her. Fortunately, it was because she wanted to stand up on her own and make Nanoha-mama proud of her.
In the third Sound Stage for this season, Reinforce Zwei finds a recording left behind by Reinforce Eins that shows her living with the Yagami family, then a message saying that this is what she gave up when she sacrificed herself, and while Eins knew it was the right decision, she regrets not being able to be with Hayate.
That one part in the second opening where Nanoha is running towards Vivio as they both desperately try to reach one another, but their hands fail to touch by a few inches.
In the second ending sequence you see Nanoha juxtaposed with her younger self. There's a certain melancholy to seeing the optimistic little girl grabbing her older self's hand before fading away.
Four words: "You're not my mama!" Nanoha is clearly on the edge of tears after hearing it.
Subaru's Heroic B.S.O.D. after she fails to prevent her sister's kidnapping.