You have been on three dates with Nadia and you really like her. Tonight you cooked at yours, the evening went well, and she has missed her last train.
You offer to let her stay, and she says yes. You have one double bed and a sofa.
The principle
Agreeing to stay the night is agreeing to stay the night. Say what the sleeping arrangements are, make it clear nothing is expected, and let the guest choose.
If this brings something up for you
You can stop at any time. These UK services are free and confidential. In an emergency, call 999.