Kindle - firstly, unmumsnetty hugs. I agree with previous posters that it sounds like you are blaming yourself for this, which is a consequence of the tough time you've had recently ... and a consequence of a lot of the nonsense about attachment that is out there, which is almost inevitably all to do with blaming the mother
. I'm a psychologist with a background in child development, so although I can't give you any definite answers on your DD, I have some points to make that will hopefully help you see that things are not as bleak as they seem.
Looking at your description of your DD, I presume that the play therapist intended to imply that your DD fitted into the insecure-ambivalent category, because of the preoccupation with departures that you mention. I can imagine that this is massively stressful every time it happens. However, since your DD is fine once the separation actually occurs, I don't feel that this attachment category accurately describes her behaviour at all (you would expect that DD would be angry, distressed and withdrawn during your absence, and strangers/teachers would find it hard to calm her/ deal with her in your absence - but that's not what you report; she's doing well at school. Moreover, you would expect her to be reluctant and withdrawn when you return, but as far as I can tell from your account of events, this doesn't happen either). This says to me strongly that the issue is not with attachment.
Attachment, contrary to the initial implication of Ainsworth/Bowlby et al, is not all or nothing. Their system is categorical, but a big study of 12-18 months old indicated that instead there is a continuum of attachment behaviours and relationships. To think of attachment as dichotomous (secure/insecure) is simply misleading to parents: this is not the way that we see development take place in real life. Children exhibit different attachment behaviours between time and situations, and with different caregivers. And it is very important to note that children themselves actively contribute to the construction of the relationship with the attachment figure - temperament has a big and often neglected role to play in this.
It is pretty hard to measure attachment in the older child, and indeed there's no really reliable way of doing it. It's certainly not a diagnosis in the way that the term diagnosis is usually understood i.e. carrying implications about aetiology and prognosis, implying a categorical difference from a different, non-pathological state. Your play therapist needs to explain why she thinks this explains your DD's behaviour and, more importantly, why it is helpful to frame your DD's behaviour in these terms i.e. how should it inform interventions and strategies? If, after explanation, you think this IS a helpful way (for you and for DD) to understand her difficulties, then that's brilliant. If not, however, don't feel like you're rejecting a 'diagnosis' - attachment theory remains just that, a theory, with lots of ongoing debate about it. Feel free to question what you're told, and remind yourself that you know your DD best. Have you and the play therapist discussed separation anxiety? It sounds like your DD is struggling with this rather than anything else, and the good news is that with loving support, this tends to decrease with age. Finally, do ask your GP for a referral to a different source of psychological support for DD if you feel it would be helpful - something like cognitive behavioural therapy can be very useful in this kind of a situation, and most children tend to find it fun and confidence-building.
Wow, I've written an essay. I hope some of that's useful ...