Two things have helped me in the face of loss (though I have not lost a horse yet and neither one of these things eases the idea of ever losing Lacey and maybe you've already heard these things): one is a statement/saying by Dr. Suess - "Don't cry because it's over, smile because it happened" (aka, focus on the good times, write those into your memory with indelible ink and don't focus on her end) and the other idea is that to heal, you have to embrace your grief. Don't push these feelings aside or down because they aren't "logical" or "rational" - give them a voice, let them out.
I think the things you're feeling are perfectly normal. You're grieving the loss of your best friend = perfectly normal.
Take a day, do nothing, just watch some stupid TV, read some books, cry if you feel like it, don't push yourself to be "normal" because things aren't "normal" right now. Give yourself time to grieve and honor Indie's memory.
Sure, she wouldn't want you to be sad but to move on from sadness, you have to grieve fully first. Don't be embarrassed if silly things make you tear up, that's perfectly normal! Just take the time to think about why you're crying (or feeling like crying) and honor it.
And I don't blame you if you want to punch me in the face right now. I probably would want to punch someone in the face if Lacey had passed and I was told that stuff. But it does help eventually and the pain does eventually lessen.
Take your time, keep our chin up, you'll be ok.