Subleaser gives 1 day notice and is suing for damage deposit, help please

The situation:
I lease a duplex and rent out 2 rooms with no lease agreement, only a verbal agreement that 30 days notice or more be given in order to find a new tenant for the room.

1 renter pays month to month, often giving cheques 3 months in advance due to being out of town. March 13, renter says she needs her Apr 1 cheque back (I already had) and will write me a new one ASAP because she's closing her chequing account. I give it back, she rips it up, and then she hands me a written note saying she will be leaving Apr 13.

I talk to her and tell her I need 30 days from the end of the month and ask what she planned on paying for her half a month she intends on staying. She refuses to give me an answer and ignores me. I tell her I will use her damage deposit of $400 to pay for it. (Rent is $550/month)

She does not speak to me again until March 30, I come home all of her stuff is gone and there is a note saying her last day will now be today and she wants her $400 back. I talk to her and say I will honour her mid month notice even though i dont have to, and try to give her a money order for $150. This is the difference of her damage deposit, less half a months rent. She refuses to take it, says she wants it all or she's taking me to court and leaves. The room is vacated without doing any walk through, she has not cleaned the room at all and has left dents and scuff marks in the walls.
She hands me a civil claim form today, and I offered again to give her the $150 money order, and she refuses.

I want to know if I have a valid claim in that I have WRITTEN notice for the 13 and kept 1/2 months rent, because she changed her mind on the last day of the month without talking to me and agreeing on anything. I also don't know how much court costs or anything is.

I don't know whether I should fill out this civil claim form and write in a counter claim amount, or if I should just give her the money back and then sue her seperately for a full month's rent because of the lack of notice.

Please help.

By the way, this is in Alberta Canada. I don't know if it makes a difference. Maybe.

She will lose. She has to abide by the notice terms you agreed.