But if this and all our other information is not enough for you to feel yourself 'well prepared' and certain then you always can decide to provide yourself with more information, tools or services.
It's you who has to make the choices, but making the wrong choice can cost you a lot of money.
Ask specific questions and check if you receive answers on these questions In case you are using an Agency with email forwarding or other mail-services, and your correspondent is not responding on your specific personal questions, this could be a sign of being suspicious.
Another important thing is to confirm with her if your (original) letters indeed are reaching her.
One of my favorite quoted expression is: "By failing to prepare, you are preparing to fail." (Benjamin Franklin - 1706-1790) But there are also many variants, that are 'close' to swindle practices, but not (yet) labeled as real illegal organizations.