Here we go, then.
As has been said in this thread, gaining a position as an AP is pretty hard. She should feel very happy that she's got an interview with 'just' a degree. I don't mean for that to sound harsh, but the likelihood is that the other interviewees will have MSc / PhD. That's not to scare your girlfriend, it's a reality in this business, but she must have 'something' if she's got an interview. So, well done first of all.
As for the actual interview; it all depends what the AP role is doing - is it in Education, Clinical, etc? The important thing to remember is to answer what's asked, but make sure it is domain specific - if it's an education based post, then we need to answer in an education-based way. Seems obvious, yes, but it's VERY important. A lot of people see psychology as one core subject - it's not. It's lots of little subjects rolled into one and her answers should reflect this.
I.e; As an AP, how do you feel you would be able to support the child/adult/offender/special needs individual? If the job is education based, the answer would be... 'I would be able to provide education based psychology support by (a) implementing strategies to promote success for the individual, (b) liase with other agencies / school staff to ensure the best support is provided for the child and (c) be able to mentor and be a positive role model for the child. I have experience of doing this from my work with Autistic children....and example of how I have done this is......'
Hope that makes sense.
Don't go in and blurt out all the things she will have learned on her psych degree. They will
know that you know that stuff. Academic psychology is very different to applied. Don't say, for example, 'I would be able to support the child because I have a large knowledge on the works of John Bowlby'....in the real world that means nothing.
RE: the presentation. It obviously depends on the topic, but i think it's important to see the big picture. If, for example, the presentation is how to support / help an adult who keeps getting sent to prison for violence, then the answer isn't 'by giving him some anger management training'. It's more about a holistic approach to each person - what's his home life like? Past life? Family support? Dependencies? Basically, there's more going on than 'he is angry'. It's the job of a psychologist, mostly, to provide support, but sometimes the area of support is not as obvious as it may seem.
Finally, really big up work with Autistic kids - Sams (as a sam myself) - not so much. They will be impressed by sams, but generally it should not be seen as a CV improving role. Basically, they will see it and be impressed, but don't answer everything with 'In my role at Sams...' because they won't like that. Emphasise how she has developed links with other agencies, and that she knows when psychologist intervention is not appropriate, and the person should be signposted to another agency - social services etc.
Lastly, good luck.

Hope this helps.