When I was growing up, mum's cake batter was always smooth with a consistency like honey -- enough to pour in to the caketin. Now I'm living out on my own, I'm cooking for myself, including cakes. But my cake batter is much stiffer and thicker than I remember mum's being: I always have to scoop mine into the caketin; it won't pour. Now, I don't recall what method she used, but I'm using the creaming method. The cake still bakes just fine. But am I doing something obviously wrong?
Again assuming you're using the same recipe...
I don't think you need to leap to different kinds of flours as in mrwienerdog's answer. You could be using the same type (probably all-purpose) and even the same brand, but purchased and stored somewhere else; it'll end up with a different moisture content, and perhaps fluffed differently, so your volume measurements might not actually end up getting you the same amount of flour.
If you're trying to follow her recipe exactly, there's really no harm in simply reducing the flour a bit to get the texture you remember.
Along with the above comment from ElendilTheTall, I would also ask what kind of flour you are using. I would almost assume from your post that you are using the same recipe (and this is why you are confused as to the results). The biggest mistake people make in baking is using the wrong kind of flour. Often, people use all-purpose flour for everything. That was okay twenty five years ago when that was all that was available, but now there many types of flour are available to consumers at the retail level. The big difference: protein count. The protein is what becomes gluten when mixed with water (and is worked). An all purpose has about nine per cent protein. Cake flour has about 4 or 5. This means that you will have much tougher cakes when using AP flour (more gluten formation). It works in reverse as well. Bread (strong,bakers) flour has about 13 percent protein. If you use AP flour for bread, you will have less structure, and a smaller, denser loaf. First lesson I learned: all purpose flour serves no purpose.
If you are indeed using the same recipe, try getting a lower percentage flour like cake or pastry flour. That is a step in the right direction.