The Church does not forbid either parties or weddings (or wedding parties, for that matter) during Lent. Catholics need to use their own rightly-formed judgment in choosing activities that are appropriate to the penitential nature of the season of Lent. So, for example, a Catholic might choose to attend those parties that are in some way a social obligation (e.g., family birthdays, company events) but forgo, for the duration of Lent, partying for the sake of partying.
