Articulating feedback as behaviours

I would really appreciate some advice on an issue I’m having with one of my directs.

She joined my team 11 months ago as a graduate trainee and after 3 months with my team, has spent 3-month assignments with two other teams (to get a more broad-based experience). The formal feedback from both was not good, they rated her poorly. The feedback also chimed with what I and other team members had observed previously.

Two main concerns came to the fore: she appears to take longer than we would expect to learn skills, i.e. asks for help from colleagues several times over where others pick it up after one explanation. Perhaps we’re being too harsh comparing her to others (esp. as I have another graduate in my team who is a rising star).

On the other hand, she sometimes does not ask questions when she should, resulting in work that on the surface looks professional, but when read, does not demonstrate to me that she has really understood what she is saying or doing, resulting in rework. Perhaps, again, we’re being too harsh as she has moved around teams.

My boss is aware of the feedback and she is not keen to have a ‘future problem person’ on the team. A number of phrases have been uttered such as ‘she’s not cut out for it’, ‘I’d expect more from a graduate’ and ‘is she a square peg in a round hole?’ I feel this is vague and unhelpful.

I’d really like to get this onto a more behavioural based footing and look at the coaching model to get things back on track. However, I’m really struggling to articulate the bad feedback in behavioural terms (e.g. what she says or does, or her work output).

Could anybody help me articulate in behavioural terms the ‘issues’ above? Would the coaching model be the right approach to address them? Thank you!