Costs of S21 court fees......Tenant fees or not...?

General Discussion

My single parent tenant has three children, two girls and one boy living in my two-bedroom house. As her children are getting older, she needs a three-bedroom property and has been on the LHA housing waiting list for three years. My tenant has asked me to write a letter to the LHA stating the property is no longer suitable as she has children of different sexes sharing the same bedroom. I'm certainly not getting involved with this as its between my tenant, LHA and Social Services so declined to write any letter. However, I did suggest that I could issue a S21 which she agreed to and I have subsequently issued and my tenant has passed this on to LHA to hopefully help her case.
Due to the high demand in LHA property, I can see that LHA won't find her a property until my tenant has received a court order or bailiffs turn up which off course would mean costs to me.
My question is, can I charge the cost of the S21 court application fee and if applicable, bailiff’s cost’s, to my tenant or are these classed as tenant fees which are banned under the tenant fees act?
I've taken the decision to sell up as each one of my properties becomes vacant but do not want to go to any expense, but in this case, I’m trying to assist my tenant and she will be willing to pay the S21 fees but I don't want any comeback by accepting fees from her if they are banned under the tenant fee act...