attachment post foster-care: is clingy always a prob?

I'm concerned that our former foster daughter may not have developed a strong attachment to her mother since being reunited with her, and I was hoping someone here could enlighten me as to whether I'm misreading the situation or if not, what I might be able to do to help. We fostered Baby V for 10 months, from the age of 6 months to 16 months. She has been back with mom for 9 months now. Five months ago, mom gave birth to her second baby, and it turns out that it was too much for her to handle, and the baby went to live with her father (the girls have different fathers; Baby V's father is now out of the picture). We stay in touch and babysit V every few months, usually over the weekend. DSS case has been officially closed and there are no more services being provided and no more involvement from SWs or CASA. The concern is that V seems to have an enormous attachment to me. It is surprising that she would remember me at such a young age after months go by without seeing me. She's usually a little shy at first, but once she warms up, she clings to me for dear life, crying bloody murder when I leave the room, and certainly hates being dropped back off at home. She enjoys playing with my DH as well, but given the choice, she tends to go to me. At first, it was flattering, but now I'm starting to worry that maybe she has not developed a strong enough attachment with her mom, who just recently turned 18. From my observations of mom and V, mom is not very affectionate, tends to let her run around and do her own thing while she talks on the phone, watches TV, etc. I've never seen the two of them play together, even when she'd come over for visits and I tried to model for her how to get down on the floor and play. There are occasional quick hugs and kisses, so perhaps she's just not a very touchy-feely person, whereas DH and I were very physically affectionate and V may have gotten used to that and misses that. It hurt very bad when she left (see other posts for why), so I made every effort to distance myself from her for a while, and I am now able to see her, babysit, etc, and then drop her back off and not think twice about it. I'm secure in knowing that her mom thinks of us as family and has said repeatedly that we can see her whenever we want. I'm happy with the arrangement being only a few visits every now and then, especially since we are still trying to become parents. I no longer think of myself as a mother-figure for her (and we never did refer to ourselves as "mom and dad" but "aunt and uncle".) But DH thinks we should spend more time with her, more time with both of them, so that she'd feel better about being with mom. Is it possible that there is a problem with attachment here? Or is it just that we're her favorite aunt and uncle, and she hates to leave a good time? She also gets physically violent when anyone leaves, hitting our neighbor with a book the other day for standing up and saying bye. We think she fears goodbyes, bc the end of her time in foster care was very chaotic, with unexpected multiple moves and lots of drama. We were hoping that seeing us every now and then would show her that we are still there, that we haven't left her. That's what we've been taught about kids and their need for permanency. I don't want to purposefully limit our time together if it really might help her relationship with her mom, like my DH seems to think. What do you all think?