Although my friend is a fujoshi, it is a gift for an 18-year-old girl, so a more serious and formal gift is more appropriate. Some gem bracelets and personality pendants are good choices, and these things are more formal.
If the host really wants to give a gift based on the hobbies of the classmate, he can use some ideas on the personality pendants to highlight her more fujoshi personality. Another way is to give comics and souvenirs, which are the most practical things to give to fujoshi, but it is really not suitable to give them as a coming-of-age gift. If the host really wants to give it, pay attention to choose some limited editions or exquisitely made ones with collection value.
In addition, if the host is really unsure, and the relationship is not particularly close, just giving a gift to congratulate her, you can also customize a cake or DIY cartoon bouquet for her. The host can make a BL-related theme based on the personality of the female classmate to liven up the atmosphere, which is also good.