I'm a lefty and I agree with those who said to let her choose what is most comfortable for her. However, if she chooses the right side, it will help her learn she can use the right hand for some things and still be dominantly left. I personally have my mouse on the left side, but it's more a matter of space on my computer table (2 computers on the same table) and my right handed hubby uses his mouse on the left hand side too. I do almost everything with my left hand, except scissors, and in fact, pretty much the only thing I can do BETTER with my right hand is throw a ball. Twirling pasta on a fork is almost impossible for me. lol
It will be hard for you (I'm assuming your right handed given that you are asking these questions) to help her with writing and such, but certainly not impossible. A good way is to sit ACROSS the table from her to help her write. Being left handed, I have to do this with my right handed daughter to help her write.
I'm only 27 but they didn't have left handed scissors when I was a kid, or else they were so scarce in my area that we didn't see them, so I learned from an early age how to use scissors right handed. To this day, I will still try to use them left handed first, but when the paper folds instead of cutting, I remember to use my right hand.
I noticed someone said they were a lefty but were forced to be a righty. Pay close attention to your child's schools to be sure they do not do this as it can cause psychological and learning problems in some. It's not just how we write, bat, throw, etc. It's how our brains think and work.
Despite the occasional inconveniences now and then (much less now than when I was younger), I am glad that I am different by being left handed.