Seems like the perfect to opportunity for Rarity to babysit Twilight now that her mommy is indisposed. I guess she'd also need to watch Fluttershy.

I would still think Twilight would be sterner to Fluttershy. That she strictly adheres to a feeding schedule and Fluttershy saying she's hungry wouldn't change that. Twilight would set up an elaborate system to take care of her.
Also an actual foal does a lot of crying.
If Twilight is going to become a mother figure for Fluttershy she's going to have to abandon most of her submissive tendencies and become a lot more dominant. She shouldn't reward Fluttershy for doing things like spitting all over Pinkie Pie, she should scold her for that.
They could try to create anti-venom. The usual way anti-venom is created is to delude the venom greatly and then inject it. The small amount of poison is something the body can handle and it makes anti-bodies to fight against it. Then they extract blood from the infected subject and multiply the anti-bodies in a lab. Ironically the usual animal to create anti-venom from is a horse.

This was a much better chapter than the previous few. It was much lighter. I disapprove of the new plot line, of course, but overall it isn't terrible. I do expect that Fluttershy and Twilight will become foals and Rarity will take care of both of them. This is just a hypothesis but given how this chapter went it wouldn't be unexpected.

I am a little confused as to why the spell affects Twilight differently than Fluttershy. When Twilight cast the spell the first time, Fluttershy became exceedingly dominant towards Twilight, but with the role-reversal, this has not been seen from Twilight. From what I recall, Fluttershy was under the effect of the spell when she was being dominant. Just questions I have. Maybe I am looking too far in, or maybe I am just a fool. Whatever the case is, I will follow this story until it ends and make sure every chapter has some comment left by me.

7310792 You're not wrong about the spell affecting Twilight differently than Fluttershy. The actual answer is I thought it was cuter to see Twilight fumble a little bit at the beginning, but if you want a "cannon" answer you could say that the spell is acting differently because Twilight didn't self cast it this time she used it in exactly the way it was intended to be used. Be patient thought she's just now been thrust into the situation she'll flex some dom muscles soon.

7309995 I can see where you're coming from saying Twilight should be more stern. But it's also her first time being in this situation and it was pretty sudden to so she hasn't gotten into the groove of it yet. Also Fluttershy doesn't seem like a crier to me. She seems like the type to just whimper and cling to something rather than to outright cry. Also I was unaware of how anti venom was actually made, I've always assumed they synthesized it from the actual venom. I've seen shows where they extracted venom from a sanke and I just assumed that's what they were doing with it, I don't know why else you would extract snake venom. And yeah the horse thing is super ironic, I totally meant to do that glad you caught my super subtle joke.

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I would think Twilight would be a little more stern by default. She's a very regimented mare so she would create a new schedule in like a few seconds (which most likely isn't very practical) and act on that.
All foals cry. Some more than others but they all cry. Also Fluttershy would then be clingy to Twilight and since she still has the body of an adult mare that can get quite painful for Twilight.
One thing I wouldn't see Twilight do at all though is rewarding Fluttershy for being naughty. She would scold Fluttershy for spitting on Pinkie Pie almost by instinct. Twilight does have quite strong maternal instincts.
Maybe you can put that making of anti-venom into the story. That Twilight uses her own body to make anti-venom since she figures that because of what happened in before (in the previous story) she'll have more resistance to it. It also would feel like redemption for her failure to protect her lover/mistress/mommy. On that: the venom has already started to work so just anti-venom isn't going to help much. Anti-venom only neutralizes the venom in the body. In order to get Fluttershy back to normal they have to find some sort of cure as well. However as long as the venom is within Fluttershy's body they can't cure her as the venom will start working again.
Making a single batch of anti-venom is actually quite simple. Twilight would just delude a little of the venom with IV fluid and inject it into herself. Than wait a few days to let antibodies form. After that she extracts blood from herself and isolates the anti-bodies. She then extracts those with various techniques and puts them into an IV fluid that she gives to Fluttershy. (Anti-venom is usually delivered via infusion since it can easily be destroyed by the acids in the stomach. Direct blood transfusion can also work but they would have to be the correct blood type and the concentration of anti-bodies would be very low so Twilight would have to give several liters of blood to Fluttershy and they would also have to drain an equivalent amount of blood from Fluttershy.)
The problem though is to get a hold of a little bit of venom. They don't need much, just a tiny bit is enough but they need to get their hooves on it. They also need to find a way to restore the damage that's already done.