All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
There is no prohibition in a woman looking at her dead husband's face. The Prophet said to his wife ‘Aa’ishah: “If you die before me, I will wash you and enshroud you myself.” [Ahmad]
No doubt, since washing (the dead) necessitates looking at or touching his/her ‘Awrah (parts of the body that must be covered in Islam); so, looking at other parts is also permissible.
Going to the mosque for that reason is also permissible provided no forbidden act is undertaken such as mourning, lamentation etc.
Allah knows best.