Ah OP I’m sorry you’re going through this. She’s still very little, she’s your baby, and every week you have to send her off to your abuser, who you doubt is caring for her adequately and you can see your child is visibly distressed. I’d be beside myself too.
Is there an opportunity for you to ask for access to be supervised by a social worker or contact centre? Do you have a mutual friend who you trust to look after DD’s interests, who your ex will tolerate and who might be able to supervise contact?
In terms of your DD in the meantime ... I would do a few things (though you shouldnt have to)-
If she’s in the pushchair, pop one juice cup in the seat of the chair with her, and give one to your ex. Make sure DD can use both independently.
Lighter layers - and maybe think about what clothes you put on her in terms of “if the weather goes either way”- tights and light dresses can actually be a good option and cooler than thick trousers. No big boots, no thick jumpers- maybe a thin cardie and a raincoat.
Make sure she’s fed something that will “last” her and give her a big drink before she goes- and maybe give a tub of fruit snacks like cut up grapes and melon which have lots of water to your ex to give to her?
Is she really in the pushchair the whole time?! Poor kid. If you can, maybe clip some of those little books/ toys to the buggy, so that she has something to play with. Does she still have a nap? Can you shift her nap time so she’s likely to sleep through some of the contact? (Not very fair to your ex in normal circumstances, but he’s not doing anything with her anyway by the sounds of it).
Is your DD verbal? Can you (subtly, and definitely don’t tell her what you’re doing) record her on your phone whilst you ask her about her time with daddy? All very neutral “have you had a good time? Did you have some drinks? Did you play?”
Finally- if juice comes back full/ nappy comes back full and has caused irritation/ her clothes are soaked with sweat- photograph it the second you’re alone with DD. There will be a time stamp on the photo and you could use as evidence of inadequate care.
The examples you give aren’t a big deal in themselves but they signpost your ex’s inability to capably parent, and if, for example, she fell ill, had an accident etc in his care things quickly could be much more serious.