Patricia Collinge's comedic acting

There's a scene where Jack (Macdonald Carey) asks Charlotte's mother (Patricia Collinge) if he might borrow her daughter for the evening to guide him around town, and her response is to suggest that he take her daughter Ann. As Ann was played by an actress who was about 10 years old at the time, my first thought was that the 40's were a MUCH more innocent time if mothers sent their 10 year old daughters off alone with strange men from out of town who claimed to kind of work for the government, but not exactly. I looked at the scene again later and thought it would make much more sense if she was simply teasing him by suggesting Ann would make the better tour guide, recognizing that his interest in Charlotte had little to do with her ability to show him the sights. The problem is, I didn't really get this from her delivery of the line.

How did other people interpret this?

I think part of my problem was caused by her prior line, where she basically tells Saunders (Wallace Ford) that she has no intention of baking cakes on a daily basis for as long as it takes him to finally get around to take a picture of the process. Here too, it seems like the line in the script could have been intended to be delivered in a teasing manner, but I thought she unambiguously delivered it as if she were an irritated half-wit who truly thought Saunders expected this of her. (Think Gracie Allen at the end of a bad day.) To interpret the next line as teasing then forces you to go from seeing this woman as comically dim-witted one moment to surprisingly perceptive the next. It doesn't really make sense.

So is this bad acting? What's up here?