Schengen visa for uk resident

[lilla]

If a person who have a non-eu passport and have indefinite leave to remain in the uk.When filling in the application form for Schengen visa does she need to provide an invitation letter or proof of income when visiting relatives? Can the part to do with when entering and leaving be left blank when applying since she still don't know when she is leaving?
She also planning to visit other countries in Europe for holiday but not around the same time.