I totally sympathise, I felt the same towards both my dsk's and I've been with their dad for 7 years, I dreaded them coming to stay, hated that they treated out house like a hotel, hated that my ds took a back seat to them etc etc, but it wasn't until I came across this forum a few weeks ago that I have completely converted and realised that it wasn't the kids I dreaded but the situation and other people mainly my mil grrr. We're quite lucky as in we get on really well with dsk's mum, we did have a run in when ds was born but thats old news now and we all agree that what matters most is dsk.
I made myself read every single post on the step parenting forum and I felt really guilty afterwards, others inclusing anniemac made me realise that they are just kids and they didn't ask for this, if its inconvenient for us can you imagine how the kids must feel, I even went as far as telling dsk that we will have them over the feb half term, they do live about 200 miles away so we dont get to see them often.
Now when dsk come to stay and the old feeling rear their ugly head which I know will, I will remind myself that its just for the week and enjoy them while we can.
Phoebe30, you are not a horrible person, it's only been 2 years, it took me 7, you will come to terms with it in your own time, I think the best thing to do is just carry on as normal, you said that you do try to make an effort and hopefully she may come round, if not then put a big smile on your face when she's there.