Hi and welcome! BIG BIG HUGS, Sarah! That's a lot on your plate! Are you able to reduce or eliminate her seizures with medication? That must be scary and stressful to see your child experience a seizure!
My older SPD son wasn't diagnosed until he was in 1st grade, but it was a relief to realize all the things that happened when he was a baby were probably sensory related. He was also a colicky baby and for the first year he would sleep only on me or touching me in some way. He has had major separation anxiety his whole life (almost 10 now)--he's very attached to me. He would scream like someone had stabbed him when the sunlight was in his eyes. He would cry and cry when I vacuumed. My younger son was a pacifier fiend, even the lactation consultant said he had one of the strongest sucks she'd ever seen. And he would scream like I was hurting him, every time I changed his diaper. I learned to change him as quickly as I could! He still prefers to eat all his food with his fingers (6 years old).
One thing I was so glad that we did was do sign language with him. It was only the basics, but it definitely helped us communicate with him. I had seen two of my nephews not talk much until after they were 3. One of them threw dreadful tantrums because no one could understand what he needed or wanted. My son is 2 years younger. So I started signing with him, thinking it was a boy thing to talk later. I knew only the alphabet and hubby's sign language was very rusty (had a previous coworker who was deaf), but I bought a couple of the baby signing books and learned from those. We just did ones like eat, drink, more, all done, milk, cookie, banana, etc. I started at 10 months old but he didn't sign back until he was 13 months old. But I'm sure if you started now with your DD, that she would pick it up quicker than that. Then we signed with him until he was talking better, around 3 years old. We did signing with my younger son, but he didn't need it as much since he was talking in paragraphs by the time he was 2.
Of course, once my kids were older and talking better, then they came out with these signing videos (wish they'd had them a few years earlier!).
http://www.amazon.com/Signing-Time-First...36&sr=8-11 I've seen a few of the shows and they're very good! You should pick up a couple of board books to try with your daughter. Something like these:
http://www.amazon.com/Meal-Time-About-An...36&sr=8-15
That should reduce her tantrums and your stress, at least about communicating. As for the other things, yes, it's going to be hard to know the difference between a normal 2 year old tantrum and a SPD meltdown, at least for a while. You'll start to understand her triggers and what to avoid. And it will get better as she gets older. Now instead of screaming his head off, my son will say, "Wow, that sun is really bright." So have hope, it will get better. But I think for now, assume every tantrum/meltdown is sensory related. Try to figure out what it might be. Sock seam not quite right? Beeping truck backing up nearby? If you figure it out, try to help. If you can't, try to comfort. Mostly just do the best you can. And figure out what things are important. Is it warm enough to go without socks? Then skip the struggle about putting them on and go without socks and/or shoes. Find some sunglasses that she likes and would wear, or a floppy hat to keep the sun out of her eyes. But obviously car seat isn't optional. Maybe try some of those strap covers.
http://www.amazon.com/JJ-Cole-Collection...B0013IEUJ0 See if that helps.
Have you started any OT with her yet? That should help overall. And the therapist can help you learn things to do at home too. Is your daughter able to walk okay with the CP?
Take a breath. It'll be okay. You're a great mom. HUGS! BTDT with the looks from strangers. Be strong, ignore them. Hang in there.