It gets worse in episode 8 during "The White Devil Incident" when she realizes that she ended up making the same mistake again.
Speaking of that, Teana's breakdown at the end of episode 8, when we see just how deeply scarred she is by the death of her big brother (the only family she had left) and the horrible things that were then said about him and their family name. After pushing herself to dangerous levels in training, the plan she and Subaru came up with and worked so hard on is foiled by Nanoha with little effort. Then, when Nanoha tries to lecture her, the poor girl finally breaks and tries to open fire on Nanoha. As she's charging up her attack, she's screaming and sobbing that she needs to get stronger, no matter the cost to herself, because she can't take losing anyone else she cares about.
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.
The flashback from episode 17 where Erio is told that who he thought were his family weren't and is taken away from them.
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.