What the fashion industry calls guipure lace and what people who make lace by hand call guipure lace are two different things
Hand made guipure really doesn't have a grain, it is worked in all directions according to the design, but machine made guipure is a yardage product which comes off the machines in long lengths and so does have a grain.
However, the structure of a lot of those laces is such that the grain doesn't have a noticeable effect on the way it hangs, and anyway if you are wanting to use a shaped edge to its best effect the chances are that you will be using a line of scallops which are parallel to the selvedges, ie on grain.
Look closely at the back of the lace. If it shows lots of (more or less) parallel lines of chain stitch then that is the grain. If you can't see that then use the lace fabric in any direction you wish.