Investigate the trees

Contrary to some beliefs, magic has rules, and it can be studied. Part of your paladin training included a basic understanding of magic principles, not to employ the power yourself, but so that you would know what to look for if it were employed against you.

If you're to recover Indra, you need to return to where the trees began attacking you so that you can study the phenomena. If you can study it, you might be able to understand it. If you can understand it, that might help you figure out who or what is behind the attack, which might help you follow their path... It's a lot of "might", but the alternative isn't really an option. Also, you need to act quickly. The longer of a lead they get, the harder it will be to rescue your companion.

With that, you set Aegis to the fastest trot you dare back the direction you just came from. The dense forest is difficult to navigate much more quickly than that, but you also don't want to ride full-speed into another ambush. Even moving a bit cautiously, you quickly arrive in the same location again, based on all of the debris scattered around.

You dismount and gingerly approach, waiting for any sign of another attack. It never comes. So it's not the trees themselves, as you suspected, and the magic that animates them departed when you left. Well, that's not quite right. Took Indra, drove you off, then it departed.

Was it covering its escape? Used the trees to attack you, took your companion, made sure you were running away... Didn't follow you. Killing you wasn't the point. Whatever it was wanted Indra. If it wanted to kill you, it could have killed Aegis easily enough to deny you your escape... but your horse was never touched...

So it hates daemons, but likes horses, and really likes Indra. Your best guess is some sort of nature spirit, possibly a dryad or nymph, which would explain its control of trees, animosity toward you, and kinship toward your witch friend. It could also be some sort of pixie playing a horrible prank, or possibly elves, though you think elves wouldn't have stopped short of killing you.

You won't know for certain until you explore further. There's no natural trail - of course a nature spirit wouldn't leave a trail - but you can vaguely sense Indra's emotions. Maybe you're beginning to bond? Well, you should be able to track her that way... as long as she doesn't get too far ahead.