May one shower before Malaveh Malka?
There is a preference not to do melacha before eating Melava Malka. Tis is a preference, but not an obligation. One who wants to fulfill this preference but finds it hard to eat Melava Malka right away can eat something, and then there is no issue with doing melacha before eating Melava Malka later on.
M:B 300-2, Piskei Teshuvos 300-5 in the name of Siddur Yaavetz (Melava Malka).