Nah, the pteranodon was the one that died on Day 6's raid. Here's her realizing it and
deciding to name her next dino Subaru 3.
And here's when
Aqua brings it to her so she can tame it.
And yeah, the renaming was on Day 6. Here's a clip summarizing it. She asked for name recommendations on Day 5 before the birth, decided on Stellar Symphony after birth, then talked with Okayu and went with ドSスイカ on Day 6:
The overview probably missed it because Subaru usually ends her stream after 6-7 hours, then keeps playing until the server closes, so she'll do a lot off-stream. Her brain basically gets overloaded and can't multitask after streaming too long, so she prefers to stay off-stream after the raid ends. Afterwards, I basically hop around through the girls' POVs until I find her lol. And yesterday, she only streamed an hour cause she was exhausted after the pregnancy arc and her throat was hurting.