Sorry. It sounds like you gave it a true honest effort to find her, which is commendable. A deer hit in the guts will die. In a few days you may smell her and then can have some closure at least to where and how far she ran. It's hard to say if hte 4 wheeler scared her, depends on if deer are used to them and you were on a road they are common to. It is a bad feeling now, but time eases it a little, and you gave it a hard search.