Witness for TR1

I am in the process of selling my property. My co-freeholder has signed and returned their TR1. As a witness they have used their 'ex-daughter in law' (who was widowed following the death of my co-freeholder's son). Her ex-daughter in law is also mother to my co-freeholder's grandchildren. 

Will this TR1 be accepted by Land Registry or must she sign again obtaining a new witness?

Thanks!

Christina - we recommend that people don;t use 'family members' as witnesses but it's not generally an issue of that happens in the way you have described. 
See section 2.1.2 of our PG 8 for guidance on how a deed should be executed/witnessed by private individuals