Legal advise needed for affidavit

I wish to travel with my girl friend to UK from Nigeria for my PhD graduation. I do have a letter from the University inviting her on my behalf. As part of the visa requirements, I need to prove that she has family in Nigeria which she would return to. For this, I intended to include an: Affidavit of Consent from her parents, indicating that they are aware of my travel plans and that they Consent that she travels and returns within the anticipated time-frame. The challenge however is that Affidavit of consent is usually issued by parents of minors who wish to permit their children to travel with another adult. As such, I am not sure if I will be correct to call my intended affidavit, an affidavit of consent. My question is, what is the best name for this sort of affidavit? Also, as we are not yet married, what affidavit would be the most appropriate to prove the genuinity of our relationship as unmarried couples? In Nigeria, Cohabitation or Common-law partnership is not legally recognized. As such, I am not able to get an affidavit of cohabitation or an affidavit for the common law relationship. I require a freelancer with expert law knowledge to offer advise in light of the raised concerns above. He or She will also be tasked with drafting out the statement of the required affidavits too. In your bid, please kindly answer the two questions asked above.