Universal Credit now have fit note

Before you do anything she needs to provide more information. Something doesn't really add up here.

Can you get her to check her account for the actual letter explaining. You need to check if it is that there is a sanction on the claim, and also that it is for missing the appointment you have mentioned and not something else.

If this is the case she should make sure she books and attends an appointment as soon as possible - If she hasn't already.

You need to submit a mandatory reconsideration (appeal) to the DWP. This has to be done within a month of the decision date.

She can phone and request a full statement explaining the decision.

You then request the reconsideration. This can be done in many ways, but the best is probably a written statement on her account explaining why you disagree with the decision or providing information they did not previously consider. Then phone or go in to check they raise it properly in her account and take in any medical evidence that she may have to support this.

In the short term she can also phone them and request a hardship payment if she's in need of money. There's no guarantee she'll get it and it will also be taken back off her future payments.