if i understand your question...
outside of crystal (or in a Command) you can create a join with an additional join clause to limit the data or an sub query in the main query with a join to limit the data set.
Inside of crystal you can use grouping and group level select criteria.
Group on Person field
create a 'flag' formula
if field1="event 1-Attendeded' then 1
sum this at the group level
sum(@flag,table.person)
In the select expert, change the select toggel option to 'group selection' and add your condition
sum(@flag,table.person)>0