Hello. I am a solicitor with over 15 years experience. I will try to help you with this.
does your daughter still live in the property?
Are you on taking terms wit her? if so why is she not paying the rent? Is there a written agreement signed by you as guarantor. The 6 month tenancy has expired what does the agreement say about your obligation at the end of the tenancy?
Do you have a copy of the guarantee agreement. It may be limited to the length of the tenancy. Even if it is not then you can tell the Agent that you are going to stop paying the rent and expect them to bring proceedings against your daughter. If it was a 6 month tenancy then they have the ability to gain possession very quickly by giving 2 months notice and then starting accelerated possession proceedings against your daughter. You would be responsible for 2 months rent and possibly the costs of evicting your daughter. If they do not take this action then they have failed to minimise their losses and you should not be held responsible for their excess losses.
That sounds like a very sensible approach.
Then they would have a first instance right to sue you for failure to act as a guarantor but you would have a defence to any losses claimed beyond 2-3 months rent + possession proceedings costs if they didn't take action against your daughter. That defence would be that the agents/landlord failed to mitigate their losses as described above. There would be a risk if they took proceedings and evicted your daughter but were then unable to relet the property that you would have further liability but this would depend on the terms of your guarantee and they would have had to to genuinely try to market and let the property.
OK. Check what the agreement says about this situation if anything because this is a contract law issue so the contract is the starting point for everything.