Nothing much to worry... Actually, some women get swollen and sore gums, which may bleed, during pregnancy. Bleeding gums are caused by a build-up of plaque on the teeth. Hormonal changes during pregnancy can make your gums more vulnerable to plaque, leading to inflammation and bleeding. This is also called pregnancy gingivitis or gum disease.
Next Steps
Get her examined if she's having unbearable symptoms, which is unlikely.
Health Tips
Warm saline rinses (Warm water mixed with salt) definitely gives relief if done 3-4 times a day. Good luck!