Si,
It is vital that you follow the correct legal procedures in this matter.
By your own admission you are happy with her work and timekeeping in general, so I would suggest that you take a few deep breaths, count to 100 and look at this situation logically.
All of us from time to time do stupid things, my advice would be to talk to her, and explain that you believe that this incident was out of character, but that you are trying to run a business, and that in the present climate, you cannot and will not allow behaviour that could lead to termination of any of your contracts.
You should at this meeting, try to find out if she is experiencing any problems at work or in her personal life, this has to be done tactfully, this could explain why she went off the deep end so to speak.
Depending on her answers, and attitude, you may then wish to inform her that this meeting should be regarded as her first verbal warning, and as such, will be noted on her employment record for the required legal period.
(This assumes of course, that you have had not had cause to issue either, verbal or written warnings to her before this)
I see many people on this and other forums, complaining that they cant find or keep good employee's, this is a two way street, there are many rules and regulations that govern the conduct of staff and employer's. Templates and other info off the net will only get you so far, there is no substitute for training, knowledge, experience and respect.
Hope this helps.
Regards,
Rob
