Thank You for your patience. Because the girlfreind has paid no rent she is not a tenant in law, you can change the locks and deny her access to the property as of right, as she is merely a lodger subjject to the true owner's right of possession and discretion as to whether she stays. You can bag up her stufff and and ask her to collect it, she has no remedy in law as a lodger.
If she is resisting these peaceful attempt to oust her there is a court process to oust her in Delaware.
This process is expedient and usually takes 20 days from the time of filing.
You bring an action for summary possession in the local justice court.
After winning the action a writ of possession will be ordered and the girlfreind's sunsequent attempt to gain access to the property can brought to the police's attention.
Landlord tenant law in Delaware describes this action precisely
An action for summary possession in accordance with § 5702 of this title shall be maintained in the Justice of the Peace Court which handles civil cases and which is closest to the premises or commercial rental unit and in the same county.
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BEST OF LUCK