According to USCIS, she can enter on a B-1 visa for this purpose, but she needs separate employment authorization. Furthermore, information online suggests that she may also need a specially annotated visa, in which case she may not be able to use her existing visa.
The following types of B-1 business visitors require employment authorization:
• A ...
You cannot chain together visitor visas to achieve, in effect, residence in the UK. If you have a visitor visa with a duration of more than 6 months granting multiple entries to the UK you may not remain for more than 6 months in any rolling 12 month period.
"You can stay for a maximum of 6 months on ...