Is the client effectively buying advertising for their business? If so, and at first glance, I'd say yes.
There are HMRC rules to be checked out (particularly Notice 701/41 in respect of VAT and BIM42565 with respect to admissability) but your client's intentions sound simple enough not to attract any objections.
thank you for your replies, she is not vat registered so don't need to consider tht part. it was more of a sponsorship than anything else, where she paid a cheque at an exhibition.