Lactating goats do not have a fully functioning immune system, and they are under huge nutritional demands. It is very important that she gets drenched .... if there is any reason that you thinks she needs it, such as "bottle jaw", runny poo, or less enthusiastic for food and looking depressed.
Look at what the ingredients are for the drench you are using. The drench family that has the -ectins is very safe, the -azols are very safe, and prazanquantel is safe. If the drench only has these drenches then you can safely drench at 1 1/2 time the amount you would give a sheep, and repeat the drench in two or three days.
If the drench has levamisol in it do not overdrench, and wait seven days before repeating. Levamisol is quite good at getting rid of our goats worms, but it is hugely less safe than the other families.