Ok, yes, Bec is right, you can't PUPD and then stop to feed. That will just tell her that if she cries for long enough, eventually you'll feed her. However, you don't have to make her go all the way til morning if you don't feel like she's ready. If you want to start with the 4 hr interval, that's a good time, I think, esp as she's not taking to solids. So, you'll need to PUPD until she falls asleep, even if it ends up going over the 4 hr. Then, even is she sleeps for only 20 min, you can feed her when she wakes again. So, basically the 4 hr time limit here is your reference (not when you'll feed her, iyswim); if she wakes before it, you PUPD and don't stop until she falls asleep.
I personally wouldn't move her crib to the dining room. If she's spirited, I think that's likely to just make the whole process longer. Is it possible for your DH and DS to stay with friends or family for a night or two while you work on this? An alternative would be to get some white noise for both of them, so hopefully they can sleep through the crying better. And remember, PUPD isn't the only option. If she likes the shhing, you can use that while rubbing her back or stroking her forehead as well. Basically, you're just trying to soothe her without feeding her to sleep and then you can gradually wean any patting or rubbing that you may need to.
Without a CN, the last A of the day is really too long, which is why Bec asked about that. She's ending the day OT, which is going to make it harder for her to settle in the middle of the night. It's pretty normal at this age for them not to have the CN anymore, but you either need to let her nap for longer or go for an earlier bedtime. Are you waking her from naps to keep to the 4 hr routine. If so, I'd let her go for up to 2 hr at each nap and that should get you to a 7/7:30 pm bedtime. Or, if the last nap ends at 3/3:30 pm, I'd shoot for a 6:30 pm bedtime.
(((Hugs))), sleep training is definitely hard work, but you're right, think of how much more you'll be able to enjoy her and your DS once this all gets sorted.