Asklemmy

Ask her what her favourite episode is. Once you get small kids talking, it's actually great, they tell such great stories.

Share (age appropriate of course) opinions of your own along the way. Like, don't just say "have you seen [episode with pots and pans]", expand it by saying stuff like you've not seen much Bluey, but you have seen the one with the pots and pans — does she know the one you mean? I suggest this because kids are actually pretty socially adept and I've found myself in analogous situations where I caused confusion by mentioning something I barely knew and the kid reasonably interpreted this as "this person wants to talk about this thing", and then when I didn't seem to know anything about the topic I had suggested, the kid seemed pretty thrown off and uncertain how to respond.

Or completely open ended questions, like "I know you like Bluey, but I've never seen it before. What's your favourite episode?", which could lead into asking for more details on what happened in that particular episode and why she likes it.

The thing about small talk is that I've found there's a distinction between being good at it, and enjoying it. I used to think I was awful at smalltalk, before I realised that actually, I just didn't find it enjoyable. I think to some extent, the point isn't to enjoy it, but to build a conversational back and forth rally which builds initial rapport to figure out what common ground exists between two people (which can lead to more enjoyable proper conversation). Some people do enjoy small talk though. The rally model was useful for me because it underscored how I need to serve the other person options to hit back with.

For example, most kids go to school, so that's a decent enough topic for if you're running out of ideas. With kids, you can get away with clunky conversation starters like "What's your favourite subject at school?". Better than that though is something like "My favourite subject at school is science, what's yours?" because it gives your conversation partner the option of responding either to your statement (such as with "ugh, I hate science, [teacher] is so mean!"), or your question, and having multiple options to hit back with allows for flow to help. Once you hit on a topic the kid is excited to talk about, you're golden: just keep being interested in their perspective and give bits of your own perspective so they don't feel like they're being interrogated.

Edit: This was a great question, btw OP — It's led to a lot of interesting discussion, thanks for asking it