Side note to Peter Rehse: The one thing that cannot be assumed is that those beginning aikido -- or any martial art, for that matter -- are already physically fit.
Also, she did not stop to 'take a slower role' because, quite simply, she's new to martial arts: she trusted to the discretion of the instructors as to what was safe for her to do, since they're supposed to know better when teaching beginners. This 'mistake' could have sent her to the hospital -- or, worse yet, to the morgue. (Then they would have had to deal with me. :P) Just thought I'd clear that up.
One thing I like about Aikido and Budo in general is that it doesn't make pre-suppositions about fitness level, budo experience, confidence and coordination. Try joining a sports team at your average North American university as opposed to ANY martial arts club and you know what I mean. I watch all my beginners very careful no matter whether they are slight shy women or Dan ranked TKD people (I have them both). All get pushed but according to their ability. I say this just to be clear that I'm not coming from a "its the beginners fault" perspective.
Two comments before I continue.
I come from one of the most physically demanding Aikido dojos in this country which also happens to be a neighborhood dojo. Alongside 40 year old housewives train world class athletes whose bread and butter is full resistance randori. Everyone feels comfortable - and no one demands those that are less physical go the same place as the big boys.
One of my pet hates are dojos that don't train with resistance that consider themselves tough by how hard they slam down compliant uke's. This is garbage. I don't mean that uke must be gently guided to the floor surrounded by mood music but uke must be taken into account. You can train hard without causing injury.
That out of the way - I can only comment on what's written here. Based on what Selkie wrote I just offered a contrary point of view - quite kindly I thought. Every so often we get posters that decry how mean and nasty a particular sensei is - my point is that in Budo training, although allowances should be made, we are responsible for our own training.
If this dojo is dangerous for your friend - she should get out. The one thing worse than a careless teacher is a student that doesn't recognize the danger signs. That has nothing to do with experience in Budo but plain common sense.