Well, unless she's a "touchy-feely" type of person (hugs people in the corridor, smiles and waves to almost anyone or her friends) then touching her lap is probably normal for her. If she isn't, then she may well be feeling the same way. At the end of the day, you can only know if either of you say or do something.
I know that seems daunting but at least you'll know where you stand. If it goes in the direction where she doesn't feel the same way, then you can always try to remain friends (however, it may be awkward at first - speaking from personal experience but it gradually wears down eventually), chances are, you'll respect that and you'll probably won't be "lusting" over (or rather, fancy) her so much.
On the other side, if it does, then you try to find out where you want this to go.