I don't remember number of hours/day that we allowed our son at that age, but he has always had mostly unrestricted access. We ended up getting him a netbook when he was almost 4 because at that time he was wanting to use my computer frequently enough that we had to compete. Now he's been getting back on mine again because he likes to print out maps and sports logos and the latest is that he has asked for his own printer.
I do tend to be a bit more wary of TV time rather than computer use, which might be a personal bias, but I don't think it's as interactive and doesn't allow them to pursue their own interests as easily. That having been said, guess where my kids are right now? LOL
If you're concerned that there's too much electronic usage, which I'm guessing you may since you're posting this question, I'd suggest you see if you can cut back on what she's doing in the car and instead listen to music or sing together, play I Spy or the Alphabet Game or something like that instead.
