Building Local Support
One NGO visiting a donor office may not put very much pressure on the organization (unless you are an influential organization yourself!). But numerous NGOs doing the same sends a clear message that there is popular concern about the issues you raised originally.
Consider reporting your initial meeting to your NGO colleagues and to the community in general. If you think it appropriate, you could hold a briefing for your colleagues with the members of the delegation reporting on the way that the meeting went.
You should encourage your colleagues - and community representatives - to also pay a visit to the donor. This provides you with the opportunity of promoting the human rights approach analysis that you conducted and may elicit new information and different perspectives.