I have booked flights on Easyet for my sons girlfriend and daughters.I have entered her details with "Mrs" she says she is an unmarried "Miss".Shes 29 years old. Would the checkin staff refuse to let her fly.All other details are correct, spelling etc.
I doubt it will make much difference so long as her passport name matches the booking name. If in doubt you can e-mail easyjet and ask them, they aim to reply within 48 hours but I have found them to be much faster than that.
I flew last week and on both mine and my mother's boarding cards we we entitled "Mr" instead of "Miss" and "Mrs" respectively. It really isn't going to make a great deal of difference. They are always making typos themselves. As long as you have spelt the names correctly, you should be ok.
If you wish to change it, I believe this is one of the changes they do not charge for. I did it wiith an online booking and went back to change it later which was allowed.