My daughter seemed to sweat as a baby a lot more than my son ever did...especially her head. I think it's just one of those things that differ from child to child. It will help to fold up a receiving blanket and put it under her head wherever it's resting against your body. Because there's a lot of heat in skin to skin contact (even with a shirt between you), having a buffer there will help immensely.
My daughter is three now and I still have to do that when we cuddle. I remember before she started using a pillow, she'd leave a HUGE damp spot on her mattress where her head rested at night, even when her room was very cool. I eventually realized that it was the "plastic" feel of the waterproof mattress that was making her sweat..and the thin sheet wasn't helping. So I put on a mattress pad and even layered a thin blanket over that (underneath the sheet) so that there was more breathable space between her head and the mattress and that seemed to help a lot.
I also started turning her ceiling fan to run backwards (sucking the air up instead of pushing it down) so that the air would circulate in her room better without directly blowing onto her skin.
Even though a sweaty head is perfecly normal, try and watch for signs of true overheating like flushed skin and heat-rashes. Also if her neck and/or armpits feel damp (when she's not being held), she's probably too hot and needs to be dressed in less clothing or kept in a cooler environment.
But as long as you're taking these basic precautions, I wouldn't worry too much. Some people just run a little hotter than others. In fact, if it only happens when you're holding her, YOU could very well be the "hot" one. If she could, she'd write a message to babypedia.com and ask if it's normal for mommies to sweat so much against your head, lol.