Hi,
Firstly, thanks for reaching out! It means a lot that you are willing ro invest in this. I wishyou were one of my colleagues!
I would agree with others above in regards of don't panic! Being an adopter involves a lot of people asking a lot of questions (sometimes more or less sensitively), so it may be that she is just used to giving short precise answers. Sometimes it's better to be clear (read:blunt!) because hinting often means people don't pick up what you are putting down, and don't think about what they say.
I agree with people above in that generally avoiding comparisons of children to what you think is normal is good.
I was thinking about why she might have reacted to your comment about full time working, and was wondering whether maybe it's a touchy subject. As she said, you need longer with adopted children, and it's a commitment, especially if there is a job you love. Giving up work, going part time etc means that you know you will have to sacrifice this, and there is a grief associated with that, which comes with defensiveness and frustration. Knowing that other colleagues have the ability to go back to work full time, and she may not for the next 18 years because her child can't tolerate child care or school or whatever might be really hard to accept. The loss of professional identity, overwhelmed from being with the child, jealousy that someone else is being promoted, guilt that she values that AND her child... its complicated.
The topic you asked about was questions to ask to promote a positive relationship, so in addition to water cooler talk (who doesn't like to gossip about Love Island?!), if family comes up I would possibly pursue a couple of the ideas below:
Family traditions that they are establishing (pancakes on Sunday, football games, arts and crafts after school etc)
Focus on similarities between yourself and your child in non genetic ways- "Oh, my child copies his sassy look from his mother" rather than "well that's from his mother's side"
Good local amenities for children
Weird hobbies or interests kids have
If you do want to talk about adoption itself:
Depending on how close you ultimately become, she might want to discuss the process of adoption. I know lots of people I've spoken to about it are shocked by the length and level of it, as well as the myriad factors involved. Some people don't like to talk, as it can be personal, but an interest in the process itself rather than the child might be something to consider.
Usually curiosity with an available out is good- so saying things like "Oh, that's interesting... i don't know much about that" or "hmm, I hadn't really thought about...." "is there a difference between adoption in the USA and the UK?" Etc
A general comment on films or media- "since you mentioned adoption, I've realised it's mentioned everywhere!" (It really is!)
I know you haven't said any of these, but for future reference, these are things that might be sensitive and require a little more thought:
Birthday and Christmas celebrations- lots of AC find these hard
Age related expectations
Obviously the "real" mum comment (notafictionalmum on Insta is an interesting follow if you are interested!)
Your experiences of knowing a neighbor's uncle's cousin who adopted- all adoptions are vastly different, and it's hard to know that you are also being discussed in these terms
Being overly positive and cheerful about adoption, or responding to stories of child abuse lies Kyrell Matthews with comments like if only he had been adopted- it's not helpful, and you won't know the child's birth story, so avoid drawing parallels
Anything about how lucky the child is. If they were lucky, their birth parents would have been able to keep them safe and parent them well.
Finally, I would say that if you know you have privilege, you should consider how to use if for the better. The person probably doesn't want to be the flag waver for adoption, but just like being LGBT, often if you are out and open you suddenly become the go-to person. Maybe you could consider, if asked about company policy or someone else makes a comment as above, taking responsibility to shift the conversation or challenge something without being prompted by your colleague?
I hope I haven't been too OTT in these, and obviously play it by ear, but I hope these are useful signposts.