You can learn to express them yourself if your cat is okay about you handling her bottom. I can express my dog's anal glands, but I wouldn't be able to express my cat's.
It does sound like that could be a possibility. In that case, it's best to take her to the vet to have it expressed.
In the future, you can observe her poop. Normally, anal glands are expressed naturally whenever they have a poop. However, if the poop is soft for a long time, then the anal glands won't get that 'push' from the pressure of the poop. So the fluid will get stopped up inside. It can also be hereditary as well.