guarantor is pulling out

Hi , I have a LHA tenant single lady with 3 kids since 3 years. Rent is recently increased through section 13, and have already paid first increased rent.
I assumed that once rent is renewed , the guarantor's contract wont be valid, am i right there?

I am happy with the tenant as i never had late rent and always looked after the property. but guarantor wants to pull out, nothing i can do right ? so best to let her on month to month ,what do you say ?

Thanks