Question: Please help me. Red spot on larvae?!

Please, I'm so worried about my little larvae, she/he's not been doing too great at all.. She/he's 6 days old now and has developed this thing.. it looks like a blood blister or a red dot. At first, I stupidly thought it was just me being able to see her belly being full as I'd read that sometimes they get little orange bellies, and it was so faint in colour that I just put it down to a nice full tummy. But over the past 24 hours it's become more pronounced and red. It's definitely not a full tummy, it's not even in the right place for it to be the stomach!
I'm so stupid, please could you help me to figure out how to save this baby? This little one has lagged behind it's sibling since birth - what have I done wrong?
I do 100% water changes every day with fresh dechlorinated water, that's at the same temperature as the water they've been in. I make sure there's always plenty of daphnia in the tub (there's not many in this tub as I took them out to get better pictures) and that they are kept at a cool, stable temperature 16-17c.
She's swimming real strange too.. swimming up, thrashing about, then floating back down. I mentioned in a separate post about how it seems the daphnia are attacking this baby, as if they're trying to eat it, instead of being eaten themselves.
Can someone please tell me what to do? Tell me what I'm doing wrong to make this happen? The other baby is fine, getting bigger, developing more colouring and seems to be content.
How can I go so wrong with one baby and so right with another? I don't understand what is happening or WHY it's happening.
Please just help me to save this baby, I'm so attached already it's ridiculous.

Hi i don't now what that is. You could stick him in clean clear glass. Then you can get a better picture of its side and a good look at its belly. Could be something in its digestive tract.

A clearer picture would be great.
I doubt very much that you are doing something wrong. I couldn't see very well from the pictures, but where on the body is the spot located?

Is it the mark on the back? Is it a raised lump or a flat mark?

My baby didn't make it, he/she passed about 45 minutes ago. I couldn't do anything to save him/her. Never felt so bloody useless and helpless in my life. It must have been my fault somehow, babies don't just die for no reason, surely?
The blood spot was slightly raised last night, as if it was an actual tiny blood blister, on his/her side, on the top. I'm sorry my pictures weren't very good, they were the best I could get without stressing the baby out even more by moving him/her again. I didn't want to risk it. Maybe I should have and now this wouldn't be the outcome. Ugh.
This red mark literally appeared out of nowhere, seemed orange at first, got darker and more pronounced within 24 hours, proceeded to become raised and end my baby's life in less than another 24 hours. I feel like an absolute monster.
& I know I only had him/her for a week but I got SO invested, so attached (I'm sure I must seem pathetic to most of you) but I really wanted this larvae to make it and have a long life.
I failed, and I really, desperately hope my other baby will make it. This one seems stronger, is bigger and quite content but I've heard that things can go wrong in such a short amount of time and now I'm just praying that everything will continue to go well for this little baby.

I'm sorry if this post isn't very good or understandable, I'm really upset right now and I'm probably not making any sense. Thanks to all who've replied to my threads with advice, tips and well wishes, I'm sorry I failed at keeping this little one healthy.

Happens to everyone raising larvae at some point and in some way. They say 50% of marble newts die during embryo stage. Something about tail growth. I dont think anyone can stop this because of genetics. Read about raising larvae on this site. They talk about spinners no one can stop that. Maybe they are bait so some others can get away in the wild. Not a good feeling but we don't live in a forgiven world. I'm very sorry about your loss. Best of luck with your other one.

I'm so sorry to heat that your little one has passed away. I find it unlikely that it was something that you did. As Chris mentioned in the other thread, they do have a high mortality rate. If you consider the amount of eggs an axolotl will lay each time, it allows for this. Unfortunately, as they are utterly adorable as soon as they hatch and steal your heart immediately, it doesn't make it any easier for you.
You are not a monster, please try not to beat yourself up over this.
Take care.

Thank you both. Fingers crossed for my remaining little one.

I'll keep my fingers crossed.