Payment Gateway Question using Square

On one of my forms I have an integrated payment widget using Square. This section of the form isn't mandatory & up to now I haven't had a client put in their card details.
As I mentioned to the client it's part of a policy for new clients & if there's a no show it states I can take payment.

I had a client last Thursday who put in her card details with the full amount of the treatment cost. I saw on the form that it's a pending charge. After the treatment she asked about the charge on the form. I replied that the pending charge is only there in case of no shows & that no payment has been transferred. I did a separate manual charge with my Square reader while she was here. I did not click the link on the form.

She contacted me today stating shes been charged twice. I checked my Square account & there's only 1 transaction. I've now gone into the form where the widget is & I've read this "Authorization Only. Authorize the card now to charge it manually later. Expires after 6 days". 

I've asked at this stage where she's seeing this 2nd charge. Haven't had a reply yet.

Am I right in thinking that this pending charge will expire in 6 days (which will be this coming Wednesday). Is there some way I can cancel the pending payment prior to the expiry?

Just found the widget. It's Square Integration.

Thanks for your help.

Am I right in thinking that this pending charge will expire in 6 days (which will be this coming Wednesday). Is there some way I can cancel the pending payment prior to the expiry?

Yes that is correct. "Authorization only" charge will automatically expire and customer will not be charged. It is like a temporary hold on the credit card which is released after its expired. 

On your question related to manually cancelling the authorization only payment, I will have to check it in Square dashboard. I will test this and will get back to you if I am able to find any option.