Your question is very important and you will surely be enlightened. First of all, it should be understood that thrush is a common problem in women and especially young women who are in their transition stage from a teen to a mature adult. This is a common problem and is a simple type of infection which has a genuine treatment that can eradicate this infection permanently. This infection is characterized by a swollen vagina and problem in the urinary tract which gives a burning sensation in the vagina while urine is discharged. In some cases, the vulva of a woman swells up and that could be more painful. As for your young friend it is advisable for her to share her problem with her parents and get a fully check up done, because if this thing is ignored for a longer period then it can develop into something uncalled for. The treatment is subtle and easy and should be taken as early as possible. The lump formation usually happens when the vaginal tract is not cleaned properly and it is not kept healthy by proper conditioning of it. To tell you about any sexually transmitted diseases that can take place if sex is done without the help of male or female condom is quite evident that an unprotected sex is not advisable to any couple who are not engaged in relationship shell. In other words if sex is being done for the purpose of pleasure and the sex partners are continuously changing then one should do it with a condom only otherwise sexually transmitted diseases spreads far more quickly if the vaginal tract receives different kinds of male sperms fluid in a short period of time. Thus, it is an advice for your friend to get a medical examination done and encourage her to have a protected sexual intercourse for her safety only. Good luck for you and your friend have a happy and safe sex life.