How many times have you tried to introduce one new veg type in the month you’ve had her?
What other items have you tried with her?
Some pigs are a bit fussy with veg and some just need more convincing!
I assume the boar is neutered and that they live together in the same cage? Does your boar eat other veg? If so, she may learn from him. A month of having her isn’t very long.
Have you access to fresh, dog pee free grass? That also contains vit c and as their natural diet is the reason they don’t make it themselves.
If you have access to some grass then that usually goes down very well! (Introduced very slowly on an unprepared tummy so as to not cause digestive upsets).
Pellets do contain vit c - have a look at the pack you use to see how much is contained per serving (although pellet packets tend to suggest a serving size much bigger than should be given). It can also degrade over time if the pellets are open too long, but it may help you to work out whether she is getting enough from those and then from whatever veg she will eat. Lettuce may be a lower vit c food, but it does still contain some.
Signs of scurvy include rough coat and poor condition, weight loss, being in pain (including dental pain), reluctance to move and difficulty walking (piggy may hop like a rabbit), swollen joints, diarrhoea, internal haemorrhage.
In milder cases where it is insufficient vit c but still getting some, they may just be generally unwell.
When you say red feet, is it spots of red under the skin or are the feet red in an even amount all over?
Are there any open wounds on the feet? ie bumblefoot
Red feet which are evenly red all over can just be due to being warm (they regulate their temperature through increased blood flow through their ears and feet), so on its own I would not automatically attribute that kind of redness to scurvy without further symptoms and vet diagnosis.
I’ve seen on your other post a few days ago that she is five months old.
You said on that post that she is eating fast and is constantly bloating. Has that been resolved? Bloat is a very serious condition and requires vet care. If she is having issues with bloat, veg would need to be removed from the diet during a bloat episode.
If you are worried she is not getting enough from her diet or has any level of vit c deficiency then you should consult your vet.