A 3 yr old should be able to play independently, but for an hour is asking too much. My 3 yr old will play for about half that time, only if her 5 yr old brother is not home. When they are both home it is much harder for them to play for any length of time and get along. 15 mins tends to be about it before I need to speak up to mediate some kind of disagreement between them.
When I had a baby and toddler, I used to keep a special basket or bag of toys that were reserved for times I really needed my older one to be occupied without my involvement. The novelty helped keep him interested for longer than all the toys that were available full time. I made sure these special toys were only available every couple of days for a limited time, an hour or less, so they'd hold the novelty for a bit before I had to switch them out for something else.
I also started rotating toys once my 2nd was born and I needed my 1st to be more independent. Same idea, keep things novel and interesting. You may also do a temporary toy swap with a friend.
Also, TV is extremely limited in our house, I like to have multiple TV-free days each week and only watch a half hour on the days they do watch, with movies being special occasions. This lets me use tv as a "babysitter" when I need to. Since my kids don't get much of it, they are entranced. TV watching for my kids is very strategic on my part.
Also, kids get creative when they are "bored" so you don't necessarily need to jump in to redirect when she is looking for something to do. Give her some time and she'll figure it out.
Oh, and my kids LOVE to have jobs. A little hand broom to sweep crumbs under the table, old socks on the hands to dust, a spray bottle of vinegar and paper towels to shine a window, folding wash clothes, matching socks, washing dishes...my kids love to work. Give her something to do that will help you and make her feel grown up.