If she returns to Canada before her PR Card expires, she may be allowed to enter. If she is allowed to enter, she can stay here until she meets the residence requirement, and then apply for a new PR Card. If she is allowed to enter she will not be deported. If she is allowed to enter, but renews her PR card before she meets the residence requirement, the government may try to revoke her status.
There is the possibility that the could have her status revoked while attempting to enter Canada.