Sorry about the slow reply... The shock of weekend sunshine
Solutions
Do not apply for a visitor visa, you can't do it in the UK in any event. It would be a trip out of the UK to return. If you use this route you actually make things worse because the future extension of the tier 2 would cease as they would have to apply from outside the UK with a restricted COS etc etc. Which will be in a year time because of the cooling off period. So under no circumstances leave the UK at this time.
Best option... Sit tight they have 28 days grace period after visa refusal date or visa expiry date whatever is the latter before they become an overstayer. They can't work but that will give her employer the time to get another COS so she can apply again. New application with fees etc etc... They can't escape that. I am assuming her Sponsor does not have any COS on hand?
The employer could try to speed up the COS allocation by speaking to UKVI. Do not hold out much hope in it doing the job.... But sometimes it can help
If you want to waste money seek to appeal the refusal, it is a futile action, won't achieve anything and won't help her situation either going forward.