Yes this is possible.
Just edit the course and set the force previous unit/quiz complete setting to "No", refer:
http://prntscr.com/bt4tgs
Now students can see any unit/quiz without marking the unit as complete. However to finish the course she has to mark all the units as complete.
There is an alternative to this also, please refer this tip:
https://wplms.io/support/knowledge-base/auto-mark-unit-complete-when-open/
It will automatically mark the unit complete once the student opens the unit. Therefore when the students sees all the units she can directly finish the course.
Let me know if this helps.