Do you know much at all about this "breeder", obviously they wouldn't be a registered breeder, any registered breeder would know better than do let a 5 year old pregnant cat go to a new home, let alone the fact of her age. I.e is the "breeder" well known in your local vicinity, if so you may be able to ask around a little and find out a bit more. It is irresponsible and concerns me greatly. Believe me I know the situation you are in and that it is not your fault but the person who is "breeding". I fully suspect that it wasn't a planned breeding at all and that the female got out without being spayed and a local tom cat had his wicked way with her. Then once the owners realised...they wanted rid as too much responsibility for them (even though the responsible thing would have been to get her spayed).
Makes me incredibly sad and concerned. I would not take the "breeders" word for it that your cat has any bengal at all in her. In fact, quite the opposite as the others have mentioned. She doesn't look like she has any bengal in her.
The way a kitten is going to turn out is always a surprise, you can get some indication on seeing the mother and father, but as you haven't see the father, it is impossible to know.
I hope she is doing well, just keep her comfortable, make her feel secure and unthreatened.
We are all here for you to help in any way we can
xxxx Mia